You can slicken up the process for doing this. You'll get anomalies along the way whilst you're in the process (sync and show outputs etc) of course but consider...
1. Apply licenses to standby and reboot it (check your config, including default roles).
2. Failover to your standby.
3. Apply licenses to the master and reboot it.
3. Failback to master manually is not automatic (config dependent).
Assuming you're not doing a code upgrade, failing back to the master shouldn't be too impactful.
If you're applying PEFs, you'll need to be mindful of the consequences of this work of course. Note that the user roles and connectivity experiences may alter from what you had before. We'd need to see your whole config to validate.
What you're doing is a major system upgrade, so the business expecting it to be seamless is a big ask.