In theory you could... just buy a storm bolterpowersword as your two other wargear slots, leaving one for the 60 point suit of terminator armour.
On the other hand, right-thinking GM'sPlayers would probably not do so... although for varying reasons.
As a player, it's a poor idea, as there will be a *large* number of scenarios where it's just not practical to use. And as you can only get Artificer armour as wargear,NOT via requisition points, this means that you've just got standard power armour for those missions. Whereas someone 'buying' artificer armour can then just requisition terminator armour as required.
As a GM there is more than enough grounds for saying 'no'. Terminator armour is supposed to be very rarevaluable. Given that the Deathwatch have a very limited number of suitsa large number of Marines, it makes little sense for them to ring-fence a suit for someone to borrow on a permanent basis. Much more sensible for them to just loan it out to whoever needs it the most, instead of letting someone hog it!