Not entirely sure what you mean, but I think If-functions will give you the answer you need.
if (v12 > .1) v13 = v12.
this says: if the value in V12 is bigger than .01, give v13 the value of v12.
2 pieces of advice:
- save a temporary dataset before you start playing around with these things.
- think very well ahead how you want to combine the variables. Be very specific in the "rules" you want to use (e.g., in the example above: what do you want your new variable to say if both v12 and v13 hold a value?)