The SET PARAMETER ID and GET PARAMETER ID statements are used with SAP memory to pass data between two separate transactions, each running in its own session.
When you use SET PARAMETER ID to assign a value to a field, opening that field later will retrieve the value you previously set.

Now get parameter id
If you enter the data in that field and hit enter you will get the value of that field entered.

Output:

I think this is not how PARAMETER ID is intended to be used. For transfering values from and to memory you should use MEMORY ID (EXPORT TO or IMPORT FROM).