Hi
I have tested the following in my lab.
1. MC7030 running 6.5.4.14
2. Upgraded the Partition 1 (not in use) to 8.5.0.6
3. Use the AP preload feature to preload 8.5.0.6 to AP connected to MC7030 still on 6.5.4.14
4. After Preload was completed I disconnected the AP and booted it with console connected :
apboot> osinfo
Partition 0:
image type: 0
machine type: 48
size: 10627500
version: 8.5.0.6
build string: ArubaOS version 8.5.0.6 for 30x (p4build@pr-hpn-build09) (gcc version 4.6.3) #74058 SMP Fri Jan 24 02:34:58 UTC 2020
flags:
oem: aruba
So If I understood your question correctly it could work.
Cheers