I want to change the button text from next to install once the user accepts the license agreement. Clicking the radio button of accepting the license agreement should change the text of the button from next to install.
There are no hooks that will allow you to change the text based on a event on the license page but you could change the text when you first enter the page:
Page license "" licshow
LicenseForceSelection radiobuttons
Function licshow
GetDlgItem $0 $HWNDPARENT 1
SendMessage $0 ${WM_SETTEXT} 0 "STR:$(^InstallBtn)"
FunctionEnd
or you can use LicenseText "" "$(^InstallBtn)"
If for whatever reason you feel you have to do this you can try the button event plugin...