There are two ways to copy alternatives
If alternative 2 is set to based on alternative 1 for everything except create plants, which is set to "use alt 1", it is possible to copy alternative 2.
If alternative 1 is copied, and not other changes are made, leaving two alternatives with alternative 2 set to "use alt 1" for all possible field, the file size will increase significantly.
After copying alternative 1, if you wish to set rooms to "based on alt 1" it doesn't matter where you right click in alternative 2
If you wish to copy an alternative to change the glass type in all rooms and compare them, which option would be the simplest but would still work?
Set templates to "based on alt 1" and change the glass type in the templates
Set rooms and templates to "based on alternative 1" and change the glass type in the templates.
Set everything to "based on alt 1" and change the glass type in the templates and rooms
Set rooms to "based on alt 1" and change the glass types in only the rooms that have glass.
Select the best option to use for the following scenarios:
You lose points by selecting incorrect options. You may leave an option blank to avoid losing points.