Help With Overriding One To Many Relation

Howdy, 

I have two db tables. A project with Title and Description, and an asset with a place for a GUID that references a project. One asset can belong to one project, but one project can relate to multiple assets. Pretty straightforward.

I'm looking to have a page on the backend that lets me see and manipulate this data. I have about 5 days of experience with sitefinity 6 and need to get this out the door. My idea, with limited knowledge of my toolset here, is to use the multi-select field control (dynamic something something, its a thunder template for one to many relations, sorry i don't have the project in front of me right now) but on submission I'd like to, instead of passing the list of guids, simply find the assets they relate to and update each asset's RelatedProject value to the Project I'm modifying on the backend. Is there an easier way to do it than this, if not, can you let me know where I would have to do the overriding as I can't seem to find the code for this backend page. Thank you.

Please let me know what you might need from me, in case I wasn't clear enough. Thank you in advance.