SCPL , I don’t agree that you are on the receiving end of CASA retaliation for heading overseas. Merely that in your long absence, rules changed. Governments come and go, legislation changes.
Many years ago I headed off to Blighty to experience the whole European flying thing. I already held what was then a British Colonial ATPL, having had it issued in Fiji, which was still run by a satellite version of their CAA. But the Pommy CAA made me sit ALL the ATPL exams and would not recognise any Type Ratings that had not been gained by passing their ARB exams, so I had to do a couple of those, too, to become employable.
Once I got that out of my system I went elsewhere. I kept the UK ATPL going for nearly 30 years. Then the Brits went all Euro and along came JAA, EASA etc. End of the UK ATPL, unless I went to the expense of heading back there, doing an Instrument Rating renewal etc to swap it over while it was still valid. Did the CAA keep me informed of these changes? Nope, it was entirely up to me to know how I could be affected.
Now the Poms have the possibilty of Brexit meanng they may have to reinstate their own licence.
It is quite possible you could get a CASA ATPL on the basis of an obsolete SCPL. BUT, you will then have to do a full MCC at considerable cost. When doing licence conversions the Authority does not allow ‘cherry picking’ of qualifications from various sources. They only allow equivalence of one licence. The FAA, NZ CAA etc are all similar in this regard - only one licence and its associated ratings etc is allowed for consideration in any conversion process.
Either way, you will have to do the flight test in a multi crew environment. What you need to avoid is the additional burden of the MCC course.