Variable Substitution

Hi

I have some doubts regarding this

1) Can we use source file name in Variable Substitution ? And when we use source file name, then do we have to check ASMA always ?

2) If the file name is in the source then will it always appear in the target payload ? When we use file name from the payload, then do we have to check ASMA ?

3) When we use Variable Substitution , do we always have to set the " Disable Security Checks " indicator ?

Radhika