If you want to debug Smart form in non-modifiable client, then you can debug Smart forms Function Module using session break point.
Step 1: go to transaction SMARTFORMS and provide your smart form name, open it in display mode
Step 2: expand the page, select code, and copy its name i.e. %CODE35
Step 3: Test (F8) smart form
Step 4: now open this function module in display mode
Note: Whenever a form is activated a Function Module is generated
Step 5: find string %CODE35 which was selected in step 2
Note: Instead of using (Ctrl+F) short cut uses this option.
Step 6: double click on search result
Step 7: place session break point wherever you want in your code
Line number 1867 triggers when user dev01 executing the smart form &line number 1870 triggers session break point for all users.