If you have to ask wether your code uses one of those 20 variables, you propably don't know what variables we're taking about. In paragraph 3.3.1 of the documentation (
here), you can find those variables, ranging from $0 to $9 and $R0 to $R9. You don't have to declare/define the variables, so you don't have to use '!define'. You can, however, use 'StrCpy', found in the documentation
here.
If you want to use one of those 20 variables 'twice', use Joost Verburg's code above.
You might already know this, then ignore my post.