you can build them yes, but that does not mean that they will work the same. i don't know about HBS's game, but in MWO they changed heat, damage, and range mechanics a little to facilitate balance (or to placate players) so a design that works well in MWO will be odd in BT.
for example, most MWO custom designs are massively oversinked. because heat is vented in an over time rate, the more heatsinks you have the faster your heat goes down. also, because they made DHS vent only about 50% more heat instead of double (to help keep laser boats from dominating)
also, light AC's like AC2's and 5's actually end up with better damage over time than a heavy AC.. their lower cycling time between shots means that a person with good aim can often inflict more damage over the span of a given time than the lower ROF heavy AC's.
PPC's and lasers kinda fall into similar issues.. because lasers fire over a length of time their heat interacts with heatsinks a bit differently, and of course since range is handled by a damage fall off system even weaker lasers like the Small and mediums can be used to tag people at extreme ranges (they just do minimal damage), so large lasers are not as popular except where hardpoint limits limit laser options. PPC's use splash damage (small amont of damage ot one spot, then damage to surrounding area) so their lethality is measured differently, etc.
they also altered the ammunition numbers, weapons get more shots per ton, and they added half ton ammo for everything, not just machineguns.