to copy use the lorica hamata legionary for the first cohort:
1) backup descr_model_battle.txt
2)open descr_model_battle.txt
3) look for roman_legionary_cohort
copy the lines
Code:
texture romans_julii, xc/data/models_unit/textures/ferres/TIBERIAN_COHORT_JULII.tga
texture romans_senate, xc/data/models_unit/textures/ferres/TIBERIAN_COHORT_SENATE.tga
model_flexi_m xc/data/models_unit/ferres/ROMAN_COHORT_high.cas, 15
model_flexi xc/data/models_unit/ferres/ROMAN_COHORT_low.cas, max
4) look for roman_legionary_first_cohort (just below it)
5) replace the texture and model lines with the ones from the legionary entry.
It MIGHT work by just replacing the texture IIRC but I'm not 100% sure of how good it looks.