Beware, Be wise, Be happy
Of course having someone do it is easy and a fine option if that suits you but I would agree with tenders.
As someone who is hands on with all my boat projects (I want to know the ins and outs of everything aboard) and speaking from experience in this matter, I would caution against doing it youself while in the water, epecially if you are installing a feathering/folding. But I would encourage you to do it yourself.
I've recently installed a 15" two blade Max-Prop and setting blade angle and pitch is challenging on the hard with two hands. I couldn't imagine doing it in the water, not impossible but not something I would want to attempt unless in a dire situation. I did it on the hard with 4 hands and 4 eyes on the manual, haha.
That being said it is a project that I think anyone is capable of and would encourage you to do it yourself. I would just spend a little for a short haul and if you are installing feathering/folding read the instructions thoroughly beforehand.
Additionally, if your prop has been in the water for any period time, it will probably not just slide off. There will have to be some "negotiations" which should not be done with a mallet. Not only will you potentially bend you original prop but you could bend the shaft or damage the cutlass bearing. If you have to give it a "tap" for any reason you should be sure not to touch the blades.
To make the removal easier I would suggest you purchase a bearing puller. A tool you can find an most automotive suppliers. Should only be around $30.
I hope that helps and wish you luck with your project.
-Chris