Are you trying to edit the code in the form itself after dragging the form into the editor? When you do this, it creates a div tag that notes it's an eloqua form and every time on a fresh load it would refresh the code in case any changes in the form asset itself has changed.
There is a work around to this is to find the div tag that contains the form that has something similar to below:
"elqid="123" elqtype="UserForm" elqformname="UntitledForm-1508536219068""
Take that out of the first most div tag holding the form and it won't overwrite the code. However, that means if you were to change any fields or form validation in the form asset, those updates would not carry over so only do this when you've absolutely completed your form. Let me know if you run into any issues on this!
Hong Tai Lee
I wouldn't recommend removing the outer tags around the form itself. You may think a form is done but have to come back to it later, only to find it disconnected. Or worse, someone else that doesn't realize it is disconnected stumbles across it.