I have a exo-terra mat, now it says that it needs to have to backing pulled off and stuck onto the surface. can i stick it to a piece of polostyrene so i can move it at a later date if need be?

I think they are intended to be stuck to the underside on the outside and could therefore be pulled off and relocated (even if with great difficulty). If you have an exoterra type terrarium where there is a gap between the base and the support area it would be OK but it would be a problem on an aquarium type terrarium because the base would nor be supported properly and the heat would be trapped and may cause the base to brake because of differential expansion. That is one of the reasons why I don't use heat pads.

I have a exo-terra mat, now it says that it needs to have to backing pulled off and stuck onto the surface. can i stick it to a piece of polostyrene so i can move it at a later date if need be?

are you asking if you can apply a heat source to a piece of polystyrene?

the exo mat says it needs to be stuck down to a surface, does this surface need to be a stand or can it be a xtra piece of wood or foam that i can move as needed?

Heat and foam or plastic don't mix well. If you trap the heat by not having ventilation underneath or by puting the pad under a hide and you have a glass base it could crack. What is the construction of your terrarium?

is a glass tank

but i have rubber pieces to raise the tank off the stand where the mat will sit, will be .8cm of a gap between the mat and tank.

I don't know how to advise you as you need to support the tank but allow air movement to avoid overheating a portion of the base and breaking the glass. That is why I don't use heat pads. Someone with experience in using them may be able to help.

stick the mat to a piece of thin ply then place under the slightly raised tank

I have stuck it to the stand, now i just have to play with it to get the correct temp.