Sure you can issue a transistion altitude...but don't confuse it where we reset the altimeters....
Here in the states, the ATCcontrolers manual sez use Mach technique FL310 and above and IAS below FL 310.....
If you are a controller, issue a clearance such as.....
"UAL 976, Descend to FL 270, Maintain .82 until FL 310 then 280 IAS......."
In whatever city/state you are in, I'd believe the Controllers handbook would define speed technique as in the described in Paragragh 2 above.....although the FL's may be other than FL310 in other parts of the world......