Why adding a new parameter to structure is so painful!?

If i just add a new parameter to en existing structure, it breaks almost each BP where this structure mentioned. Some of them is unrepairable after that. I have to discard local changes for all files except structure to resurrect project. This trouble is at least since 4.10
May be a have done some wrong in my project?

Find unreal 4.4 modify structure there. Then come back and write what you think about its current state.

This was very unstable around 4.4, Epic already did great job patching it all. As to your question fixing those annoyances it is either not high on priority list or it requires some major rewriting.

I am also annoyed by this, there is not much that can be done. Recently i spent about week looking for reason why things stopped working, and reason for it was 3 broken connections from struct.
There is no god solution to it, sometimes making pure function to extract basic data types out of struct helps. Like struct has vector, string and float then you make 3 functions that give you those simple types as results.
But usually you make struct to not be bothered with single values.

Breaking connections is not the worst thing. In some BP variables of that structure type become invisible because of “bad type” and there is no way to fix or remove it. There only one way is restoring BP from backup.