Thanks for all the replies above!Most people get disillusioned and leave the army after 3 years in a rifle company, regardless of any premature enthusiasms for specialist roles. If the OP is strongly attracted to a particular skillset, he should possibly consider joining the relevant corps.
As for joining relevant Corps to trade, easier said than done.
Currently going through the reserves joining process, there is no Signals Reg or Engineer Reg near me here in South Wales.
Local unit is an infantry reserve unit, so thanks all for shedding some light in the subject.