I'm note sure I understand your exact need but here's my take. If you run a REXX program that calls a panel with some variable defined in the panel, when control returns to the REXX after the user has interacted with the panel, all variables are available in the REXX. Simple as that.
If you need some of those variables in another REXX program altogether, you can store those values in the shared pool with a VPUT (varname) SHARED and get it back in the other REXX wit VGET (varname) SHARED. The SHARED pool is gone if the user logs off so if you need those variables across sessions, you should use the PROFILE pool.