You can change the target exe file for ANY Steam game under the desired game's properties menu.

Right click on the game in your steam library and select properties. Once in properties, under the general tab, look for "launch options" and there will be a text field for inputting your own commands.

In this text field you want to write the full file path to your openrct2.exe file inside of quotations followed by a single space and %command%

My launch options looks like this:

"C:\Program Files (x86)\OpenRCT2\openrct2.exe" %command%

This should launch the desired exe file with the steam overlay, hours tracked, etc.

This same trick also works with Morrowind when using OpenMW, Daggerfall with Daggerfall Unity, Terraria with the mod loader, etc. etc.