Can I increase the capacity of a steam ejector by increasing steam pressure?

The short answer is - probably not - depending on how crafty the ejector supplier has been.

Assuming the geometry of a steam ejector is fixed and steam pressure is increased the following apply:

The flow rate of steam through the steam nozzle will increase.

The steam will expand into a wider cone downstream of the nozzle because steam pressure/entrained gas pressure has increased.

This leaves less area for the entrained gas to flow through.

Therefore, although the ejector discharge pressure will increase, entrained gas flow will decrease.