How can I add a user that can change all layouts and scripts except for removing the Admin or changing its password?

You can set the options to amend layouts and scripts in the Privilege Set, and those users you want to give these privileges to can be assigned this privilege set. You don't need to have the [Full Access] privilege set to amend layouts/scripts in FM7.

Get to this by File -> Accounts & Privileges ->Privilege Sets

The simple way is to set a Privielege Set to have:

Layouts: All Modifiable

Scripts: All Modifiable

Or go select "Custom Privileges..." for each of these and select what access the user should have to each layout/script and you can also specify what access the user should have for any new layouts/scripts. It requires a lot of thought about the fine grain detail, but gives you so much control