I think you mean RecordID, generated by FMP when it was created. Get (RecordID )
I don't know of a way to change that, since FMP uses it internally for various options.
Otherwise Record Number as Get (RecordNumber ) changes for each sorted found set.
You can create your own duplicated field [MyRecordID] equal to FMP RecordID at creation and then assign your field with any corrected MyRecordID if one was accidently corrected.
I'm referring to the Record Number. I've accidentally deleted record number 3697 which means all my own inventory numbers are out of synch. I was wondering if there is a way to re-insert this entry at 3697 rather than at the very end of my database. Does that make senes?
Yes it makes sense but sorting is the only way to assure that, and a very unstable way to match records, as you have found out.
Simply put a value in the New record to Replace the lost record so that it will sort to the Lost position in your found set.
PS: Record Number is variable based on Found Set and Sorting. In other words, you CAN"T sort on Get (RecordNumber) per se.
If it is out of synch with a number field, create a new record and enter the desired number into that field. If this field is set to auto-enter serial numbers, you can open up Manage | Database | Fields and reset the next serial value so that the next record created doesn't create a new gap.