Hi
H.08.98 is not a Boot ROM version it is a FW version.
This particular FW version is used as intermediate update when you want to update from FW H.07.31, H.07.32 or H.07.40 to H.08.100 or later.
As you already have FW H.10.108 then you already should have the latest boot ROM version. What you are trying to do is a downgrade that the switch obviously doesnt allow, because the older releases are not recognized.
With this switch it is not possible to update only the boot ROM. The boot ROM is automaticaly updated when the FW is updated.
HTH