Can the pilot fly IFR at night?
Of course they can.
13.1 A command (multi-engine aeroplane) grade of instrument rating authorises the holder of the rating to fly an aeroplane as pilot in command, or co-pilot, while the aeroplane is flying under the I.F.R.
No limitation there.
BTW, S.14 sets out two separate requirements for Flight by Night Under NVFR Procedures - The rules for NVFR Charter are different for NVFR Private and Aerial Work. Importantly, NVFR Charter cannot be done with just a NVFR rating, it requires a CIR holder operating to NVFR procedures.