Is the usage of read length flexible within a run and are asymmetrical reads supported?

This article describes G4 sequencing run configurations that are supported.

Yes, the G4 Sequencing Platform can accommodate flexible read lengths on each side as long as it is within the bounds of the kit configuration and allowable run parameters. For example, when using a 100 cycle kit, you can configure the G4 to sequence 26 bases on R1 and 74 bases on R2