You understood the UP1.5 files structure pretty well.
There are many posts from me to read about it, but none probably explains everything as it should.
A first example:
viewtopic.php?p=25804#p25804
Searching for "files structure" phrase also returns a lot of posts:
search.php?keywords=files+structure
But is it needed to read?
Generally, since I did not have (and still don't have) language files for all EE2 distributions, in Unofficial Patch it was a priority to develop it in a way that won't remove existing features from users (like overwriting language files). After all, languages are something that makes a lot of players love the game they play much more than if it was in their secondary (English) language. This is why the support for all language was the absolute priority, which multiplied the work needed to put into developing the patch.
As example file: "techtreenodes.csv" is not read by the game at all in UP1.5 (Normal Version). I modified it in game executables to use techtreenode5 or techtreenode6. It had to match the exact characters length, that's why in these file names letters are cut instead of being added.
the names of .zip archives are not important. As first I used a different archive name for every update, but stopped it at version 1.5.5 (because it was pointless). So as result, most of editable files are placed in db_155.zip. This file is overwritten with every minor update (usually released at least 1 time per month). The bigger file db_150.zip contains audio files (and maybe some animations? I don't remember). Generally, exploring db_155.zip is like a shadow of db.zip, just with a new structure. Obviously not all files were needed in UP1.5, so most of them are still read from the normal db.zip.
The problem about modding on the normal version of UP1.5 are frequent updates. db_150 / db_155.zip are downloaded by the installer whenever it detects that their checksum mismatches. If you are modding the game on the normal version of UP1.5, you will need to verify the content of db_155.zip after every update and update files that changed. This can sound as fun for 1-2 months, but with time it might get tiring. This is why I recommend to use the Developers Version of UP1.5 for all players who want to mod their game. Developer Version updates don't overwrite mod files. Many game crashes (and sometimes fixes) are applied to the Developers Version as well as to the Normal one.
If you still decide to mod on the normal version of UP1.5, please make sure to add the following command to UP1.5 Settings Custom Configuration box:
DontReportCrashes=1
This will disable crashes reporting. I would very appreciate it, as modders are often polluting our stability statistics (
https://ee2.eu/statistics/#launchstats ) and the number of crashes never shows the reality.