How can I customise only customer statements to remove the transaction/reference number and not in other sales forms in Quickbooks Online?

Currently, the option to remove transaction number isn't available for customer Statements, accts-fgfllc-com.

I can see the need of modifying the statements from QuickBooks. I'll take note of your idea to make sure our developers get your feature request. The Community recognizes feedback and product suggestions to make the program better. You can send this matter through your QuickBooks Online company file so our developers could take action to help improve your experience. I’ll show you how:

1. Go to the Gear icon, then select Feedback.
2. Enter your suggestions, then select Next.
3. You'll be provided a list of suggested Help articles related to your comment. You can select Skip and send message.
4. From the drop-down, choose the appropriate category, then press Send message.

If you want to delete or edit a statement, you can check the details from this link as your reference.

For future reference, check out relevant topics in our QuickBooks Articles hub. You can search for some pointers and ideas from other users. 

Let me know if there's anything else that you need about this or with QuickBooks. I got your back. Have a great day!