best way to maintain local ports tree changes

[Miroslav Lachman]

What is the best way to maintain local ports tree changes?

I am building packages in poudriere, 4 different sets for 2 archs (8 
sets in total).

I have some local ports and some changes to official ports. Now we are 
planing to do some small changes in ports/Mk too.
So what is the best way to get ports tree in sync with official ports 
tree but keep our local changes without a need to apply patches manually 
over and over?

What are you guys using for this scenario?

Kind regards
Miroslav Lachman