Changing texture in material blueprint.

I have created a minimap in my game, the image in the hud is assigned to a material blueprint, which gets its base texture from a render target.

I am wondering if it is possible to change that render target to a variable or something similar.

I basically have the same problem described here : https://answers.unrealengine.com/questions/239010/multiplayer-minimap-issue-1.html#comment-239010-form

I have boiled the problem down to setting these two variables.

The texture target of the overhead camera was previously set to the rendertarget file.
I have now set it to a variable within the character blueprint.

But in order to change the image in the HUD I need to assign an image not a texture, I have tried various methods for passing the texture render target 2d variable over to the image but I have had no luck so far.

Even then I will no doubt have the problem that the new image/texture material will no longer have the custom effects mine previously had.

So I was wondering if anyone had any ideas to solve such a problem.

Thank you in advance.