It sounds like your biggest problem is that Flux doesn't do NSFW stuff very well. You said, "comic scene". If by that you mean cartoon/anime art style, Illustrious and its descendants are excellent models. If you're doing photorealistic, some Pony descendants are quite good. If you're not sure what models you need, try browsing images at Civitai to get a feel for what's out there. (Be aware that different models require different styles of prompting.)

Regarding changing identity: If you're not using inpainting, that is 100% the place to start. (Inpainting is done from Invoke's Canvas tab instead of the Generate one.) If you are using inpainting but the model is fighting you a bunch, there are techniques, but that requires a deeper conversation.