Is it possible to control the scale for the subsurface scattering shader using a black and white texture.......and what color should i use on my texture to make some parts have larger subsurface scattering scale and smaller scale...?
Yes it's possible. There are two simple ways to do that(and countless more complicated). First is to use the texture to influence scale of subsurface scattering shader (Full white has value of 1 and full black 0,if you would use other colours only Value would be taken into account, Hue and saturation are irrelevant)
Second way (better in my opinion, cause it gives more control) is to use texture to influence shaders mixing: