How To Make Key field editable in WF process!!

Hello Team,

We have a requirement where GL number should be updated by second requester,

GL number being key field and it should be updated by requester2,

so requirement is requester1 will not provide GL number and this field should be invisible for him and requester2 field should be visible and updated by him.

can we make key field editable at second level of workflow process.

Regards

Ajay