Hello Attila,
The WS2000 has been EOSL for quite some time and prior to the AP75xx series. The answer is no, the WS2000 cannot adopt the AP7522. Strongly advise replacing the WS2000 with a new model wireless controller (e.g. RFS4000, NX5500, NX7510) that can adopt the newer AP models, including the AP7522, and retire the EOSL AP300s.
Otherwise, you can use Virtual Controller (VC) feature with the AP7522 and adopt up to 64 AP7522/AP7532/AP7562) on the VC AP7522 (no different model number, just a feature on the AP).