external power question

if i connect an external power supply from an regulated 5v board link below

and put it into the VIN pin to power the board can i still use a USB to access the board for programming while the pin is powered?

No, connect to 5V header. Add a diode from 5V (anode) the Vin (cathode) to protect the regulator.
Connecting to Vin, the voltage has to go thru the regulator. A 5V regulator can't regulate with only 5V in.