Installation

run openiv and enable edit mode, go to "pc" - "models" - "cdimages" - "playerped.RPF" and drag the files inside

IMPORTANT
Change the file number (99) to the clothing item you want to replace.
For example:
uppr_099_u.wdr = uppr_001_u.wdr
uppr_diff_099_a_uni.wtd = uppr_diff_001_a_uni.wtd

to wear this outfit, use native trainer v6:
https://www.gtainside.de/en/gta4/trainers/29661-simple-native-trainer-v6-0/