Report group / Painter Vs ABAP

Hi,

There are some tools in FI like Report painter/writer, by using them functional people can develop reports/ reprot group ( for ex: using txn GR51).

If there alreday existing Z report group. Can we modify it?

If so will it b done by Functional guys it self? or Abapers needed?

if abapers needed, in which scenario it requires abaper's help?

if abaper want to modify it, how can he do it?

Thanks

Pra