The AdditionalEngramGroupBits option allows you to unlock Engrams normally map-locked on any map of your liking. They'll be normally learnable, still in their original categories, and not be remapped. In other words, it'll be just like the map developer unlocked them for you.

The number is made up from the respective bits for each DLC

2 - Island
4 - SE
32 - Aberration
64 - Extinction
128 - Genesis

To unlock all possible engrams, just sum all numbers for the option, eg:

2 + 4 + 32 + 64 + 128 = 230 -> (Technically 2 is never needed, since that is available on any map)
AdditionalEngramGroupBits=230

The option is in addition to the natively unlocked engrams on the map. So for example to only add SE Engrams to the map, use AdditionalEngramGroupBits=4