Thanks for your replies, all good information. Seems very grey indeed! Not as defined as I'd hoped.
Using a T/R on an airbus as an example: -
On-wing (line) – Airbus AMM is the document to use, which contains inspection criteria, allowable damage limits & basic on-wing repairs just there to prevent AOGs & ensure T/R is serviceable.
On-wing (base) – If possible use Goodrich SRM, which contains more extensive T/R structural on-wing repairs.
Off-wing (base) – Use Goodrich CMM (with references to further SRM tasks) & associated VCMMs.