Here's how to do the texture switch.
1. find descr_model_battle.txt in the main EB "data" folder
2. backup it
3. open in suitable text editor (I use Notepad++)
4. search for hellenistic_infantry_hoplitai_hellenikoi
5. change these lines
Code:
type				hellenistic_infantry_hoplitai_hellenikoi
skeleton			fs_o_f_spearman						    ; combat spear
indiv_range			40
texture				thrace, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_thrace.tga
texture				greek_cities, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_greek.tga
texture				macedon, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_macedon.tga
---

model_sprite		thrace, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_thrace.spr
model_sprite		greek_cities, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_greek.spr
model_sprite		macedon, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_macedon.spr
to this
Code:
type				hellenistic_infantry_hoplitai_hellenikoi
skeleton			fs_o_f_spearman						    ; combat spear
indiv_range			40
texture				thrace, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_thrace.tga
;texture				greek_cities, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_greek.tga
texture				greek_cities, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_thrace.tga
texture				macedon, eb/data/models_unit/textures/hellenistic/ebhellenistic_infantry_hoplitai_sor_macedon.tga
---

model_sprite		thrace, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_thrace.spr
;model_sprite		greek_cities, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_greek.spr
model_sprite		greek_cities, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_thrace.spr
model_sprite		macedon, 60.0, eb/data/sprites/hellenistic/ebsprite_hellenistic_infantry_hoplitai_macedon.spr
or whatever unit texture and sprite you now prefer (for the record, ";" at the beginning of a line "comments it out" so the engine doesn't read it; this is a good way to keep the original value around for an easy "rollback" if you want to revert to the default)
6. ????
7. profit!

Also modifying the recruitement areas is a pain and a half. Don't do it unless you really know what you're doing.