I don't quite understand you, sorry - do you want to put a 20 gallon tank on a stand made for a 10 gallon? or do you want to put the decor of the 10 gallon in the 20 gallon. I wouldn't suggest you put a 20 gallon on a 10 gallon stand - the stand might not hold it. But there's no problem putting the decor from the 10 into the 20.