Define the formula in a cell based on the contents of another cell?

Google Sheets:

I'd like to define the formula in a cell, but that should depend on the contents of another cell.

Google Listing Example:
https://docs.google.com/spreadsheets/d/1Z2VVLH5saVKJQ97xUNTZ4vssXnw9Q_ruyQF61tCbxsU/edit?usp=sharing

Goal:

The change of cell "aaa" RED must define the content "changeme" on

  • "aaa", if "aaa"
  • "", if nothing"
  • "= ROUNDUP ((1 + 2) / 2)", if "my formula"
  • "= SUM (1 + 2)", if "myformula2"

Is it possible?