Spinwing
Perhaps I might refer you to EASA CS29.1581 for the legal rules in EASA land. the others are similar I believe.
Try looking for the Part 1 supplements (which cover normal and emergency procedures, operating limitations and loading information not operation and use information) for every modification that is listed in your mod record book or equivalent for your aircraft. I suspect there will be a long list of items for which there is no supplement.
If a modification does not introduce any abnormal, emergency procedures, change limitations or introduce loading changes which a pilot can influence i.e. not in the weighing report/basic weight sheet then a supplement may not be required. During the minor and major change process the need for a supplement is evaluated at an early stage this is a critical part of the determination as to whether it is a minor or major change. For clarification a major change requires an STC a minor change may be approved under other means such as the Part 21 design approval under EASA and ODA in FAA, I think CASA has a similar arrangement.