The technical parameters of WS-21 have not been announced yet and are still confidential. Judging from its performance on the J-35 series fighters, it should have surpassed the RD-93 engine by a lot.
In theory, there is no technical obstacle for the JF-17 series fighters to use the WS-21 engine. The working principle of the core engine of the WS-21 engine is exactly the same as that of the RD-93 engine, but some materials and production processes of the core engine are different. The technology of the engine accessory casing is derived from the WS-19 engine, which is somewhat different from the RD-93 engine.
That is, if the JF-17 switches to the WS-21 engine, the fuselage will need to be modified to a certain extent, but the changes will not be large.
Since Pakistan does not have a relevant test environment, if the JF-17 is to switch to the WS-21 engine, the relevant testing work can only be carried out at CAC. But we have not obtained any relevant information at present.
Pakistan has already purchased one WS-21 engine. But I am not sure what it is actually used for in Pakistan at the moment.