Yes you can, but you would not want to. 

If you need to edit it after approval is issued, then cancel the approval edit the request and then resubmit it for approval.

There’s a default businedd rule which prevents Edits on tickets when approval is requested or approved.

Thanks for the reply. My approvals are configured via a workflow and use the custom objects table. If I cancel the approval can I retrigger the workflow so it goes to all the correct approvers as per the workflow ?

Also I checked and do not see option to cancel the approval. Please do advise. I am a bit new to this tool and still learning it. 

unfortunately no unless there is something in the ticket that you could edit which would force it to find that workflow again.

Yes you can. Change trigger on the workflow to ‘Ticket updated” and then add a condition “when service approval IS NOT “requested”, “Approved”, “rejected”. then on update without an approval it will rerun