Can I interchange TIP3055 emitter & collector to avoid needing to insulate the heatsinks?
If you have the following:







simulate this circuit &ndash; Schematic created using CircuitLab

Yes it will work.  This operating region of your BJT is called "Reverse active region".  Now is it a good idea?  Well... it will work but you will get crappy performance, since the current gain will be much lower.  Also, the component may overheat (that region is rarely used and your device is not designed to be operated in that region).  It is more a side effect of BJT's internal than a real expected usage.  Usually, it is used only as failsafe in some circuits so you don't have to put diodes to discharge another part of the circuit or to do very clever circuits with very little component count.  There is no point in you doing this, really.