Hello Borislav,
it depends on the hardware installed in your router.
To make an example there was a recent thread where a colleague upgraded to an IOS XE version not supportin SIP 10 linecards.
He performed upgrade of both IOS XE and ROMMON with the unsupported SIP 10 linecards inserted,
After that the SIP 10 were lost and he could not recover them even installing them in another chassis with an older version of IOS XE.
So be very careful on what you can do and do not think that unsupported linecards are left untouched by the upgrade if any are present.
The SW procedure for IOS XE 16.9 is reported here:
https://www.cisco.com/c/en/us/td/docs/routers/asr1000/configuration/guide/chassis/xe-16-9/asr1000-software-config-guide-16-9/issu-asr.html?dtid=osscdc000283#con_1147731
You need to have two route processors to make an ISSU on ASR 1013.
Consider also the possible need for an upgrade of ROMMON to be able to boot the new image.
This can lead to systems stucked in ROMMON or even in booting loops in worst cases
Hope to help
Giuseppe
