Unwrap both halfs without applying the Mirror Modifier

I have a character wich is geometry symmetrical, but the texture for right side is slightly diffrent. Applying the Mirror will require much more work after and I am trying to avoid that. Is it any possiblity to make a diffrent texutre to the other side without applying the mirror modifier?
(hope my english is understandable)
here’s the character: http://static.giantbomb.com/uploads/scale_small/0/2779/215535-klaymen.jpg as you see, the right hand have brown fingers.

With the mirror modifier the right hand hand and left hand are in effect exactly the same mesh (that’s the whole point of the modifier) so you’ll have to apply the modifier to make the mirrored mesh real to give it different properties to the original

Applying the Mirror will require much more work after and I am trying to avoid that
Then just simply do all this work first before applying it.
Or make each hand separate objects and the left mirrored
Or apply the modifier and enable the X-mirror option for further modelling

Short answer: no.

Longer answer: It’s either symmetrical or it isn’t.

The work I wanted to do it for example rigging. So do you suggest doing rigging before texturing?
Any way. I understand Applying the mirror modifier is probably necessary.

Rigging should be irrelevant. The armature is a completely separate object and so does not care what modifiers you do or do not have on your character mesh. But as a general workflow I usually texture before rigging, essentially because I want to have one object complete before I work on another. This isn’t necessarily the best workflow in all cases though: sometimes while rigging you realize you have made a drastic mistake in topology that will cause bad deformation. Fixing this may or may not disrupt your texturing work. With more experience you will tend to either spot these problems early or recognize the appropriate workflow order for a particular project.

Why is rigging irrelevant? If I have mirror modifier I can set the deformation on one side only.