Is it possible to prevent the execution of the pulldata function while the form is in edit mode?
I believe you'll find some of the ideas in this thread helpful.
When you look up a value in an external file or choice list using pulldata or instance, that lookup is based on a value in the form. What you want to do is guarantee that the calculation only runs if the value to look up changes. You can do that using the trigger column as described in that thread.