qaqcmpm,
Have a look at this posting below or type PWHT in the search engine. A lot of questions asked on this forum have already been answered previously and it is just a case of going back and having a look.
jon20013 and js55 are very experienced with the metallurgical side of welding so you can take 99% of their opinions as gospel. The extra 1% is when jon has been partaking in a little Bundy rum ! LOL !!
http://www.aws.org/cgi-bin/mwf/topic_show.pl?pid=70948;hl=PWHT%20after%20repairIn answer to your question 2 - If notch toughness is a requirement you would have to do a second PQR as T&T becomes a Supplementary Essential Variable but if it is not a requirement then you are fine with your original PQR as T&T is then a Non Essential Variable.
In the post above js55 makes an excellent point that it is a good idea to perform RT prior to as well as after PWHT - unless you have utmost confidence in your welders or have a very,very low repair rate.
The client will be more than happy to pay for extra radiographs when he starts getting the money and scheduling costs associated with additional PWHT due to repairs,
Regards,
Shane