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Different Textures on one Character?

HI
My idea was to use different textures on one character. Is that possible without converting the texture to color? I seperated the parts of my character for the texturing process. After texturing each part, I want to apend them again. But if I apend a part, I have to convert the texture to color. That means I have to crank up the subdivision, not to loose any detail of the texture. Than all the parts together are to heavy (over 20mil polys).
If I texture the shirt for example it is enough to use a subdivision of 5 and a 2048 Texture. To hold the detail, I have to crank it up to subdivlevel 8.

Is there a other way?

Thanks a lot
Kind regards
Hilmar