The other way around, it could be done by adding this line to the defines file.
NDefines.NMilitary.SLACKEN_AP_DROP = 0.01 -- changed to 0.01; original value is 0.05
So that you lose 1% army professionalism a year for 200% manpower recovery while active.

Huh... I confess I've never considered this (as I never slacken my recruiting standards personally - rather relying on mercs in such scenarios).

So you'd prefer buffing 1% to 5% cost annually? Or the other way around?

I think slacken recruitment standards cost needs to be changed from 5% yearly to 1% yearly, it was already seldom used in current patches but with professionalism buffed there's even less reason to use it.

You'd also help out some of the people who forget to turn their slacken modifier off for a few years.

NOTE: Updated to the latest version (1.36).

Also removed the drill decay modifier for professional armies - armies with high drill and high professional effectively never decay (or decay ridiculously slowly). As such, this should keep drill necessary even for professional armies late game to ensure additional combat effectiveness (on top of their professional tier buffs).

ya I kinda agree with khaos, drill is good at the start of the war, but within the first year or two (depending on attrition), it falls off very quickly. honestly I think professionalism should give units a certian amount of starting drill upon recruitment and reinforcement, since in the base game you apparently can have the most professional army on the planet but not even give units basic training before they recruit. maybe increase recruitment time for all units based on professionalism to account for the fact that they have a longer training time.

Hmm; if enough people request a change I'll implement it ;)

in imperator rome you gain army training with siege and battle, but not in EU4. also even at 75% drill decay less. you still lose entierely the professionalism after one or two year of war. it is not the month decay the problem but the decay you have with army battle loss and siege (because even at 1% attrition, one year of siege is 12% drill less and god know how long a war not cheesy can go)

Fair enough, but I personally disagree - I find that an undrilled army would rapidly lose discipline and effectiveness over time - the 0.06 modifier loss at max Professionalism as Prussia for example is a fair balance - easy to restore them to full drill anyways!

If there was a way to mitigate drill decay/skill via active combat that'd be great, but I don't see such an option at present in the code (AFAIK)...

no the drill decay is too fast at max professionalism. if you combine max professionalism + sustained discipline (t5 governement) you would get only 58% drill decay which is very average for max professionalism

Do you mean you think drill decay is too slow?

I'm inclined to try and tweak it further.

As for siege ability, I often go for Ideas that boost siege ability so I have very fast sieges anyways. If others argue for boosts to siege ability I will make the changes.

i really don't like the max professionalism decay at max is only 25. this mean you need to stack outside modifiers just to get 50-60% decays less. 40% at max professionalism is a fair compromise.

Also no 20% siege ability is not very impressive, it is better than nothing but when we think that's a professional army in the 18th century like prussian could take a vauban fort in less than one month it was a proof that's professionalism with professional artillery was very important. also you add 10% defense at 40% professionalism. meaning with your mod now siege are even slower with professionalism which is a total countersense from historical armies.

Ok, updated now.

Update 1;

- Removed Military Tactics boost at 100% Professionalism
- Tweaked Army Upkeep at Professional Tiers to be harsher (to compensate for the high boosts). New values are as follows;

20% Professionalism = 10% Upkeep Increase to Armies
40% Professionalism = 25% Upkeep Increase to Armies
60% Professionalism = 50% Upkeep Increase to Armies
80% Professionalism = 75% Upkeep Increase to Armies
100% Professionalism = 100% Upkeep Increase to Armies

- Nerfed Drill Decay at Max Professionalism; units will now no longer maintain max Drill ad infinitum!

Hi Khaos;

Problem with siege ability is that even without mods, its still super fast with the +20% boost.

For example, I run with the Expanded Mod Series and it's crazy fast now.

By the way, what does Voltaires Nightmare add regarding Military Tactics?

@Nuggz;

I can't recall that one; this one is based off of "Reborned Military" and it seems to work well (without the hyper fast siege boosts and a few other tweaks to make it perhaps a bit more realistic/not OP).

there was another professionalism mod out that did multiple things like reduce the amount of base manpower each province actually provided, gave u like 9+ leader slots when u hit 100 (reason being that why would u have 13+ armies and only be able to recruit like 5 generals max before losing mil points), made a country lose all their manpower when they hit 15 war exhaustion to prevent that annoying 1 stack armies the AI likes to spam out after their armies get annihilated. I forgot what it was called, but not like it matters cuz i think the mod was removed from the workshop

Also i would add a bit of extra siege ability. 10% at 40% professionalisation, and +10 % at 100% so it would be 40% in total at 100 % and this doesn't make siege finishing too early compared to the original mod. so it would make late game siege faster if you have more professionalisation

remove the military tactics bonus. it is breaking with mod changing age or technology such as voltaire nightmare or extended timeline (make army insane op in early game if 100 % professionalism early)

No - if I boosted siege ability, sieges would be over in mere moments (this was a problem with the "Military Reborned" mod, where sieges would end near instantly due to the siege boost).

If enough people request it, I can see about implementing a small boost for high professionalism =)

so does this also increase siege ability?