If some one buys a second hand Lancair or RV10 from overseas they cannot do the maintenance, however the aircraft is still home built Experimental.
As above, you can indeed do this.
Any RV builder in Australia can effectively purchase an RV10 and maintain it, as long as they have done the SAAA maintenance course.
CASA’s definition of “essentially similar” points out that an aircraft with hydraulic flaps versus electric flaps is not essentially similar, so arguably an RV10 with CSU is not essentially similar to an RV6 with fixed pitch prop. That being said, it is generally accepted that if you didn’t build the component, then you can’t maintain it, so in the above CASA, it may be legitimate for a LAME to perform any required works on the CSU.