Hi Davis,
PIM accept RP can be used to tell your router not to accept just any RP. I believe it works for AutoRP and BSR, not for static RPs. For example when there are 10 routers in your network advertising themselves as the RP then you can use this command to ignore a couple of them.
ip pim send-rp-announce is used to configure your router to advertise itself as an RP, the access-list is used to advertise the networks that you want to be a RP for.
Rene