DSXchange

On the source SQL. It should be an option. Read help on the choices. You will understand why.

Does this (setting ur) have to be done as 'user defined' sql then - or can it be done on any of the other 'Read methods'?

Or should you 'set change isolation to ur' as an 'Open Command' (would that work?)

Depends on your source database and stage chosen. In SQL Server you could do a (NOLOCK) with User Defined. Some stage types have this in the options. Even though you may need a no lock as well as the option.