Mark,
repairing using a half lap on the post tops above the ties/girts is more a question of how tall is it ? if the half lap requirement of 2x timber size is longer the needed height then no, more appropriate to replace the post (yes a lot of work)
"patching" with new material after removing any decay/bug damage/etc is ok if you are not going more than 1/3 of the way into the post.here comes the Gorilla glue so the patch and the original become one. be wary of different moisture content (old vs patch). the posts are normally in compression so they are sensitive to any bending moment (normally resisted by the braces). If you are more than 1/3 of the way into the post you have effectively changed its length and the predictable forces of any bending moment become very cloudy. scotch tape and bailing wire do have their limits.
sometimes working safe takes a little longer.
am off to the Ferry Farm project tomorrow so will be away from the forum for 10 days after tonite.
deralte