Instant On - Wireless

We have procured in 2017, about 300 Nos of Aruba APs 103 and 215. These access points are deployed in various divisions of our institute. This products have reached their EOL and EOS. We are using Aruba Airwave and CPPM (Clearpass policy manager). We are an research institute with 450 Regular Staff Members and about 700 Research Fellow/Project Staff. Is it possible to replace these Apswith Aruba Instant Access Point  AP22 and AP25, which are WiFi6 capable, without disturbing our existing network.

There is not a lot of usable information in your post. Do you use controller based network? 

ION AP22 and AP25 are SMB products. It would be better to go with Enterprise product like AP-5xx and AP-6xx series.
Depend on how you would like to manage those APs, you can choose Aruba Central or AirWave or local management.
As you already have over 125 APs, Instant is most probably out of questions, hence you can use Mobility Gateway as WiFi controllers for AOS 8 or as Gateways with AOS 10.

How disruptive will be depends on how you plan to replace old APs.  AP-215 can go up to 8.6, but AP-103 can't go to version 8. 

Best, Gorazd