Looking for advise 

is the bottom skirt on rear bumper able to be changed so it can be replaced by single or twin exit skirt or does full rear bumper need replaced to achieve this 

thanks in advance 

I would think that if it is a different material to the bumper then it should be removable but whether you'll cause damage in the process I'm not sure

Then it is a case of finding the one you want, maybe removing that and bonding it on your bumper.

Maybe then it would be a case to replace the whole bumper as would be easier but would have to find the correct colour, etc

Let us know what you find out and which route is best