Yes, yes, and yes
Here are all the options:
You'll be able to switch between DHCP and Static IP on the fly, read/write your IP settings, etc. Your settings are automatically saved on the Netduino Plus's microcontroller...but you can change them at any time.
1. Be sure to update your Netduino Plus to v184.108.40.206 (or to one of the v4.1.1 betas) for best DHCP reliability.
2. Since setting the network settings saves them in Flash on the microcontroller, best practice is to only write to those settings if they have changed (i.e. after reading them). Flash has 10,000+ cycles, but they will wear out eventually if written to constantly.