first open ur Armorgtp.dat and Itemname-e from system and find from ID's the name of the tattoo...write next to the name the Stats you want them to give and after that go
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go to L2jdb and press "Armors" table..from there press search and put the name of the tattoo...check some things about them if you want to change something...after that go to C:/server/Gameserver/Data/stats/armor/
from there search the file that contains the tattoos..change what they give and save it..after that you can Start/Restart ur server and check if it works
if you mean the "tattoo of blood" and others, then you may open gemaserver/data/stats/armor/0400-0499.xml , find there your tattoos and edit they effects