Synynom for "Plug-and-Play"
You may be able to convince the users that the spreadsheet does not need to be altered if you refer to it as preconfigured.
preconfigure (v) - Configure in advance
Note that this will not stop some users from attempting to alter the spreadsheet anyway, as the word may suggest some degree of reconfigurability, but it should be enough to satisfy the majority of your userbase.
This is a turnkey solution.
From The Free Dictionary:
turn·key
adj.
- Supplied, installed, or purchased in a condition ready for immediate use, occupation, or operation: a turnkey computer system; a turnkey housing project.
- Of or relating to something supplied, installed, or purchased in this manner: a turnkey agreement.
A turnkey product is provided ready to use, and is not customized to suit the customer's needs.
Plug-and-play carries with it a lot of meaning that you're not using, here. It connotes ease-of-installation and immediate, drop-in, out of the box functionality.
But plug-and-play absolutely does not mean "unconfigurable," which appears to be the main thing you're trying to convey here.
Still, I think drop in and out of the box warrant consideration. Both of these convey that the spreadsheet/product does not need to be customized or configured, but can be easily put into place and immediately used to full effect.