You can in Asterisk, but doing this using FreePBX would be cumbersome.
You have to create a custom transport with pjsip on 5060 adding it to pjsip.transports_custom.conf (assuming you have disabled chansip and moved it off of 5060).
[10.1.1.120-udp]
type=transport
protocol=udp
bind=10.1.1.120:5060
external_media_address=xxx.xxx.x.x
external_signaling_address=xxx.xxx.x.x
allow_reload=yes
local_net=10.1.0.0/19
The thing is there is no way to assign a custom transport to an extension from the GUI, instead you would have to add the new transport in pjsip.endpoint_custom_post.conf for each pjsip extension that is on 5060.
[1234](+)
transport=10.1.1.120-udp