There are steps to take before opening a new claim, if you want to keep the previous one unlinked.
If you want to unlink a previous claim you, will to have to delete the newest claim and remake it afterwards.


If you don't want to send a claim to the accounting system -
When you have created that claim go to System > Accounting system info > Edit - Sales Tab
Tick do not send setting and go back into the progress claims list and open the next claim after the one you don't want to send
Go back in and untick this box and you will be able to leave the previous one unlinked and link the newest claim



Doing it like this will allow that claim to be unlinked for the jobs duration and will also allow you to manually mark any payment amount 
You have to create the next claim before you untick this setting or you will get error that won't allow you to open newest claim