Do they plan to replace Y-20A’s WS-18 engine with WS-20 in the future,or just leave it as it is ?
Using KC-135 as example,
KC-135A original engine - P&W J57-P-59W
KC-135E (upgrade of existing KC-135A) - P&W TF33-PW-102 engines
KC-135R (upgrade of existing KC-135A and KC-135E) - CFM56 (military designation F108) engines.
The original KC-135As have changed 2 times to more efficient engines when the old engines became obsolete. The aircraft designation changed as new engines were fitted.
Logically Y20A should go through the same path when their WS-18 engines expired after many years of usage, especially now that WS-20 engine is already available.