Custom Fields are Hardly reportable.
You can use Customer Type or Job Type. Both are fine. Now you can run Sales reporting and financial reporting and profit reporting. If you see "Columns by" at the top of the report, see if it offers By Type. Or, you Filter ON a type.
For my attached example, I filtered on Customer Type = Residential. I also could have filtered on Job Type = Only Idaho, for example, to get Both References. And you can use Subtype, such as State and then County and then City, even = to 5 levels.
I've been playing with your solution, and I see that it does make the "changes" to the job, retroactively, like I need it to for my reporting. Thank you for that bit of knowledge. Your solution brings me to a new problem....
Is there an easy way to update all the projects I have set up over the past 3-5 years without having to select and edit each one individually?