Oh you mean like how you can't put hex plates on a Magmotor, or attach extenders to the sides of motors?
That requires editing the gmf. At the end of the attachment point, there's a line that says
Attach type = Generic_F, Generic_M, Axle_F, Axle_M
If it doesn't have all four of those attach types, it will be limited in some way. For example, if you have Generic_F but not Generic_M, you can use that point to attach the component with, but you can't attach anything else on to it.
To "enable" all attach points, as you put it, just give them all of those attach types. However, keep in mind that doing so is cheating for standard bot building.
There's also Base_F and Base_M, which controls attaching to the baseplate.