Installing A/M Gauges Into Stock Sensors

Looking to add in some aftermarket gauges into my '00 Celica GT. Just curious if anyone has any experience adding the coolant temp sensors into existing engine sensors (For example, existing would be found around the oil pressure switch). I know that if the engine uses the original temp sensor for control functions, you can't really mess with it, and have to relocate it.
I saw the guide posted in the how-to on adding it to the bottom near the block drain plug, but I feel like if it's possible, adding it to the existing sensor would be a bit easier to install/troubleshoot should issues arise.

If anyone can confirm the original sensors are used for engine functions, then I will dismiss that idea and focus on installing it underneath the block.

Thanks everyone.