Yes, you can update the tier of the elastic pool on the secondary SQL Server (which becomes the primary after failover) to match the tier of the elastic pool on the primary SQL Server (which becomes the secondary after failover).
However, it's important to note that a Geo-Secondary with a lower compute size is at risk of increased replication and redo lag.
Also, you should take some precautions like you should plan the update carefully to ensure that there is no impact on the primary and secondary databases and servers. You can schedule the update during off-peak hours when there is less load on the servers.
Let us know if you have any questions or need additional information.
Thank you!