EDIT: The 1.3 version no longer needs these fixes, as far as I can tell.

I recreated my original work from a few months ago and wrote down the process this time. I don't suppose this mod has a public git somewhere? If so I could just add a merge request for @Bob.

Btw. the procedure for the Turian mod is pretty much the same; I just haven't said anything in that other comment section (yet?).
I know it's long, but that's me trying to be detailed more than any complication in the thing itself.
Anyway, here are the steps to follow:

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Step 0 (Optional): If you have a ton of mods, it's a good idea to deactivate everything except the essentials (save your original modlist!) and test with only this mod and its requirements. That way, loading times are reduced and you know for certain what mod(s) caused any issues that remain. Return to your original modlist after you got the reduced version working (no red error on startup; maybe start a colony with krogans and check that you have no errors then, either).

Step 1: Find the mod folder and make a local copy. If you're using Fluffy's Mod Manager, this is trivial. Otherwise, you need to delve into the steam mods folder (in "<Wherever your Steam lives>/steamapps/workshop/content"), which sucks, because their names are just numbers. Rimworld is '294100', and inside this particular mod should be '1793658602' (I'm pretty sure Steam assigns these IDs, so they should be the same for every install).
-> Sidenote: The Turian folder is '1783756827'.
The copy goes into your "<Wherever your Rimworld lives>/Mods" folder. From now on we work with this copy. Strictly speaking you *can* modify the original, it will just be reset if Bob makes an update or you redownload the mod from steam or anything like that.
It goes without saying that you should also make sure your game actually loads the modified copy, not the original.

Step 2 (for the Trader issue): Go to "Defs/TraderKindDefs" and open the (only) file in there. Simply delete the line near the bottom where it says
'<li Class="StockGenerator_BuyWeirdOrganic" />'.
As far as I can tell, it's something that was never defined anywhere in the mod, which is why the game complains. Presumably, it was intended contend or the creator has a separate mod that adds something like this. But not having it is better than having it not work, so it can just go.

Step 3: Back from the root of the mod's folder, copy the subfolder "Defs/ThingDefs_Races" into "1.2/Defs". Everything that follows will be done to the (once again only) file in that *copied* folder, because the change should only apply to the 1.2 Version of the game. Although now that I think about it, it's possible that the 1.1 version already had the same thing going on in HAR (Humanoid Alien Races), but 1.0 definitely didn't.
-> Sanity Check: The complete path of the copied file I'm talking about is "<Root of the mod folder copy from step 1>/1.2/Defs/ThingDefs_Races/Race_Krogan.xml".

Step 4 (based on this HAR2 Wiki Page[github.com]): Inside our copied file, find a part where it says "alienskincolorgen" and later "alienskinsecondcolorgen". Each should appear twice, once in an opening and once in a closing statement (begun with "<" and "</", respectively, for those with no XML knowledge). Everything enclosed by both of those sections (lines 145-201 and then 203-229) describes skincolors as they used to work in HAR, but no longer do. Describing how to substitute the new version is more difficult than just doing it, so I won't. Instead:
A) You can figure it out with the link above, just search for "color" and it should get you to the right section. If you have a general idea of how the XML structure works, it's totally doable. Basically, the new way is "<colorChannels> [...] </colorChannels>", and both of the original groups are contained in a list therein; see the example in the wiki link and just copy the actual colors over from the original xml.
B) However, if you don't know how XMLs work, it will probably be a struggle. So I offer you this tasty pastebin[pastebin.pl] instead. I set it to remain online forever, but tell me if the link breaks or anything weird like that. Obviously, this same code will not work for the turians, unless you want to give them Krogan skincolors. But you can still use my snippet and just change the bits inside with what you find in the corresponding 'Race_Turian.xml' version.

-> Sidenote: The placement of whitespaces does not bother Rimworld, but it sure bothers me. So if you also find the original XML difficult to read, mabye start by fixing the indentation in the affected area and it will become a whole lot more intuitive.

Step 5 (Optional): See whether you get errors at startup / ingame, and if they are related to this mod you can virtually shout them at me and I'll see whether I can make sense of them. That said, I went along with my own instructions as I worked them out again (starting from an unmodified mod install), and it did the trick.
If this did work for you, that information itself might also be helpful for other people with the same errors or for Bob to know whether integrating my crude patch is a good idea.

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I'm willing to just share my complete "Race_Krogan.xml" file, but I'm hesitant about putting it online (because of intellectual property rights and stuff; I don't know how @Bob feels about that).

Finally, have a , because I don't usually write public posts or comments and this is a rare opportunity to use some of my Emoji-.