It depends on what edits you want to make for the model. If you want just texture edits, those are simple, as OpenIV can open up .yft's (texture files for models) and export/import them (and you can preview their respective ytd's -model files- to see what it looks like) and you can open the .dds file in whatever image editing program you like.
If you want to do full-out model replacements, you need a 3D modeling program that has support for GTA V formats, such as 3DS Max 2016 with GIMS installed. Keep in mind, I haven't done a vehicle mod for GTA V, I've done only ped mods so I don't know how similar the two processes are.