Eh, if the rego runs out, there are several options.
1) Reuse rego plates.
2) Create new rego range.
3) Reg in SH/SHD series. These were originally meant for buses and
taxis.
Rego range which bus operators cannot anyhow use are CB, CSS,
PA, PB, PC, PH and PZ.
CSS-Only for City Shuttle Services, two operators, Comfort and
Singapore Shuttle Bus used this series before, registering buses in
the CSS series means that at the point of time the buses were
regged, they are meant for use only on City Shuttle Services. And
since 608 was cancelled last year, the series is basically not for
use on newer vehicles anymore, unless someone decides to create a
new CSS route.
CB (School Bus)-Mainly, for carrying school children.
PA, PC, PH (Private Hire)-Basically just for chartering, carrying
school children, Scheme B and/or adult workers.
PA, PB, PC (Private)-Basically just for own use by an single
entity.
PA, PC, PZ (Excursion)-Used by tour groups.