This requires that no jobs or purchase orders, etc. are in add/edit mode or adding that stock code whilst you are changing some of that stock's core fields.
Locking will occur even if the particular stock code is not involved in a job, purchase, etc. at the time.
This type of amendment must be done when there are no other users logged on.
Stock is Serial On sell. Someone is adding job, adding that particular stock, adding serial numbers, and whilst this is happening you change the stock to Serial not required.
You are editing the stock when someone adds a job with that stock and invoices it. You change the GL group and finish editing the stock. This will have consequences on Accounts.
The only way to be 100% sure is that, on saving the stock, nobody is adding/editing at the time (eg. no locks) and there are no stock transactions for the stock.