I'm not 100% sure, but I don't think such functionality currently exists. It seems like such a feature might cause a nightmare for maintaining libraries. You could confirm with Tech Support if your license is on maintenance.
However, it seems like what you are asking for may not be an encouraged modeling practice. Is there a reason that you need to change the Goto tag? Is it because the signal from the Goto is read in a From block outside of the subsystem? Why not simply output that signal from the subsystem instead, and connect a Goto block outside of the library block if need be.
If you are using someone else's library, can you confirm what the "Tag visibility" of the Goto block in the library subsystem is? If it is set to 'scoped', you might be able to wrap the subsystem with a nonvirtual subsystem in your model. Do not change the tag of the Goto, but use the same tag as the library uses in a 'From' block (also having visibility set to 'scoped') inside that nonvirtual subsystem. That way, your tag won't clash with others in the model.