Cant see it being someone as established as the 2 you mentioned. Based on the below Kowolik would be a 6.00 and crazily Malkiewicz a 7.50 (based on his 1.506 per race average being 6.024 converted to 4 races)
Would be someone hitting the 4.50 bracket at a guess?!
I believe woryna would be a 7.50 this year as only first season in GP but would increase to an 8.00 assessed if not signed till next year which would be his second in GP looking at assessed rules
If so he would fit as a straight swap in for lawson?!
I make it 12.91 for a general double change (taking off the 0.65 we are above the limit) otherwise yes would have to be 2 individual changes like you say