adding custom server side code box in the custom code area

Hi there,

Is it possible to add a custom server side code section to the custom code area.
This addition is essentially a replacement to adding code to functions.php of the theme I’m using.
Why do i want this change if i can add the code in functions.php?
Because I had a few functions that extend the sites functionality in functions.php and then someone updated the theme without knowing that and it caused the custom code to get wiped out.
I could create a new empty plugin just for this purpose so I thought since this plugin is for removing those extra plugins then it might be a good idea to check if something like this is possible.

sincerely,

mezo.