1. push button will triger user command event.
2. edit fieldcat table, there is a field cellstyle you can use it to set check editable or not.
3. in layout parameter set this style.
4. refresh your alv grid.
http://wiki.sdn.sap.com/wiki/display/Snippets/ALV+Cell+Colouring+and+Special+Styles
http://scn.sap.com/message/192792
http://wiki.sdn.sap.com/wiki/display/Snippets/ABAP-Changing+Cell+characteristics+in+ALV+(OOPS)
check above link, you will get what you want.