Well, I'm not sure about the name checking, but to combine 2 ram appvars A and B into C, you can do this:
Return!If GetCalc("appvA")->A
Return!If GetCalc("appvB")->B
{A-2}r->X .Size of A
{B-2}r->Y .Size of B
Return!If GetCalc("appvC",X+Y)->C
Copy(A,C,X)
Copy(B,C+X,Y)
Delvar "appvA"
Delvar "appvB"