The only difference between a continuous-duty relay and an intermittent duty relay is spring pressure and amp-draw. A continuous-duty relay has very low spring pressure to hold the contacts open and subsequently,can use a weaker electro-magnet to engage. A continuous duty relay will draw less then one-amps @ 12 volts. Also not as reliable as an intermittent-duty due to the lower pressure holding the contacts closed. That is - unless you buy a pricey one with something better then copper contacts (like silver). A continuous-duty relay can draw 2-8 amps to engage. I have seen them used to replace continuous-
duty relays and have not personally seen one fail. Just run a lot hotter and waste power.
If not sure what you have - just check the amps it takes to engage. Should be 6/10ths of one amp and maybe less.