CRM 2013 change business process flow STAGE by plugins (cross entity)

hi , i have created entity A and entity B

i have created a custom business process flow which stage 1&2 are about entity A and stage 3&4 are about entity B.

when i open form of entity A , i can see the flow 's stage 3 & 4 are locked.

now the case is that i dont want to click the default "Next Stage" button to proceed from stage 2 to stage 3.

thus, i have created a button in the form of entity A, i click it then it can trigger a plugin.

can i implement something so that i can unlocked stage 3&4 after clicked the button?

note that the plugin is already created an entity B and set the lookup of it to entity A, also its stageid and processid are set correctly to the custom business process flow's stage 3 id and process id.

thanks!

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