Do 3rd party add-ins have access to Run-Matrix in the same way Casio's conversion tool does?
During break, I plan to begin development on a chemistry add-in that would aid in calculations of molar mass and possibly approximation of change in enthalpy. It's clearly feasible to do this in a stand-alone add-in, but it would be awesome if this could be done in Run-Matrix. I doubt any program could do something as fancy as typing in an arbitrary string that correspond to an element, or even compound, but a simple menu system as already seen in Conversion would do.
Edit: I am familiar with Casio's BASIC variant and a small bit of experience with Javascript; this will be my first foray into Add-in development. Set your expectations accordingly.

Hi Juan,
I am afraid this is not possible. It seems the presence of the conversion adding works as a flag for firmware to allow conversion functionality. Simple proof: Try to create simple addin doing nothing. Just the addin structure data and icons makes this addin 28792B large. The conversion addin is 29180B large, that is additional 388 bytes. It would be impossible to compress the whole conversion logic and data (token names, conversion constants, etc.) to 388 bytes.

For example, for the Graph3DP add-in, I had to use AHelper's gCAS2 CAS to parse equations to graph; it didn't appear that there was any way to hook into the Run-Matrix CAS at all.

Thank you for your help. Hopefully I can stitch something together this break that would be enough to show.

MPoupe is right that conversion code is not in the conversion add-in itself. The executable part of it is 504 bytes and only provides nothing besides the help text and other things you see after launching it.

To make you own add-in you will need to do it in C not Basic and have SDK etc. I think C is capable to do all the computations you need without the need for RunMat as stand alone addin but will have the disadvantage of not being fully integrated with runmat...

Once you master SDK there are some limited ways of calling other programs (including sometimes changing their modes and function keys display etc) and using timers to interact between apps too. There should be a way to access and modify what is displayed in RunMat input/output area too but I cannot recall succeeding with this fully before.

Have fun and good luck