I can not speak English I have to close. translated
I feel in air problems with interpersonal communication. Do you know any other language? (without German of course)
If I good understand you unzip ALL.GSC and change value line:
Denmark AKA13DA Research granular gunpowder (firing power +15%)
Denmark AKA13DA Research granular gunpowder (firing power +25%)
After that, you pack it again and file called patch01.gs1. You run the game and it looks that all is correct. But after research that upgrade, bonus is still 15% not 25% like you want. Your question is what did you wrong (last sentence was easiest :P).
Now I will answer you where is mistake.
To change value of that research (AKA13DA) find DENMARK.NDS file. Open it and find line with: AKA13DA.
It will be look like below:
AKA13DA A13 #POSITION 4 0 #LEVEL 1 AKA13AU #COST 1 GOLD 6000 #TIME 500
DAMAGE WEAPONKIND VISTREL GRP 5 Mushketer_ev(DA) Mushketer_DA(DA) Grenader(DA) Dragun(DA) Dragun_18(DA) +15%
All what you should do is change that +15% to +25%.
You know what to do later.
UPGLIST.DAT file add to patch01.gs1 too. Now you know about that file functions.