Pizzicato in se 3?

Can I make pizzicato using the separate string section coming with halion sonic se3? and if so how?

Yes, you can use MIDI program changes to swap back and forth from your sustained tutti strings (49 or 50) to pizzicato(46),

If you want program changes to call up different sounds than the defaults from the SE Basic GM soundset, you can assign a program change to alternate programs in the Sonic SE “LOAD” Tab, down-rank the default sound and up-rank your alternate sound higher.
https://www.steinberg.help/halion_sonic_se/v3/en/halion/topics/managing_sounds/sounds_assigning_a_gm_program_change_number_t.html

OR you can load your sustained and pizzicato string programs in different slots/channels in SE at the same time, and host your sustain and pizzicato notes on different tracks/channels.

If you like, you can later freeze such tracks so the proper MIDI channels are associated with MIDI events in the parts, then slide the parts onto a single track with channel type set to ‘any’. Or, you can freeze, then merge to a single track.