Hi Richard,
I recommend avoiding to touch the core code of DNN as you will lose the ability to upgrade the platform, or at the very least it will complicate things quite a lot during upgrades.
In regards to creating your own module, that is an option, but you need to have a solid foundation of DNN module development. You get that that foundation via our module development videos. Then it is a matter of creating your own module.
At the end of the day I think you would be on a net positive if you go with Dynamic Registration module as you would be saving a lot of time as compared to develop your own module. Besides you could also ad a company name field, although you can also do that with the regular DNN feature set.
Cheers,
Aderson