I have a set of master codes, that various disciplines working on all projects need to to use for dropdowns.

I have a sheet that uses Power Query (PQ) to get master codes for dropdowns. I will copy the PQ code sheet into any spreadsheet using the codes.

Using offset etc. I want to create a UDF for the validation\ dropdown.

For maintenance, I don't want to keep the UDF in the project spreadsheet.

I would like to reference the UDF from external file.

The two (2) options I understand is:
1. Create UDF in and reference from external .xlsm file. (I could use master code spreadsheet, which is located on SharePoint)
2. Create add-in. I can enable add in when copying PQ sheet.

Which of the two options are easiest?
Are there other options?