Hence, ==> You should test specific DataWindow objects in question.
I expect you question PB 2017 R3 vs. IM 2017 R2 ==> R3 adds properties unknown to R2. So, code modified by R3 will potentially fail in R2.
HOWEVER ==> All DataWindows still not modified behave like usual. Compile/migrate for 2017 R3 doesn't change source of 2017 R2 - as long as we talk DataWindow objects.
ALSO ==> IF your DataWindow calls global functions then R2 will definitely risk problems since now we are talking about running R3 compiled code on R2. In general that is a big no, No, NO, NO!
AND ==> There is ALWAYS risk trying to open/run .PBL files compiled for different release. You need to test in your specific environment that your specific release change doesn't render the compiled code unreadable.
Anybody (like me) may direct you on anything but no recommendation beats testing!
We deliverd a 2017 R3 powerbuilder application to our customer. The customer overload our datawindows by his own datawindows designed under Infomaker R2. But he is unwilling to step from Infomaker 2017 R2 to R3.
If he have to change his own datawindows, he'll sure do it with ann R2 infomaker. But I will strongly recommend him a migration to R3.