Sandbox - apply changes on one compensation plan only

Hello,

I have created multiple workforce compensation plans.

One of them needs to be changed with Sandbox (it would be a small change, just one summary column should have value divided by another value).

I did it like this: Create and enter Sandbox -> Act as proxy -> Open the plan -> Use Page composer -> View Source and Edit -> change Output text of one column in Summary section (eligible salary, misc column etc)

When I close this and go to another plan, I can see those changes there as well.

I would like to apply such change to only one specific plan