Hi radaliendad
We are more than happy to see our user building the MakeCode extension for Max:Bot.
It is entirely OK to do that and here is a brief guide from MakeCode website showing how extensions are made.
Also, another good thing about building extension with Max:Bot is that all its functions are based on general I/O interface, which means you can simply packing up existing blocks without breaking into detailed protocols.
Good luck and have fun! Please do let us know how your geniuses like the Max:Bot and the extension.