I have just finished developing a few extensions for EE. I have noticed that when making extensions, I often end up taking code from the EE core files, and duplicating them in my extension just to make a slight adjustment. This comes down to the fact that extension hooks are placed in strategic positions, not necessarily in positions where i wish to make adjustments. Essentially, this defeats the purpose of modularization and means that I am duplicating code; and my extension may break in the future, if the core code which i duplicated in my extension is edited in a future update.

I am curious to know how other users of EE which develop custom extensions deal with this issue? i.e. do i have to rigorously check all of the duplicated code in my extensions every time an update is released for EE? or is there an actual solution to this problem?