Hi Vishal,
If your called transaction has select option then you have to use MEMORY ID addition for the select option declaration.
On the selection screen, the SET/GET ID pid will be assigned to the left range limit of the selection criterion.
And while calling the transaction before the Z-tCODE is invoked you need to GET the values.
For SAVE button issue check whether PAI is triggered or not or use global persistent memory for this purpose, once clicked SAVE update flag 'X' and then read it before your custom code.
It is a general suggestion, flow of the program is crucial to achieve the functionality 
---BR---
Tapomay