yes, the one that we see rn is them but like, after being reborn(?) again
That was their original roles, they destroyed purgatory and they were forced to swap roles essentially for 100 years as punishment.
^ A note on the comment above: after destroying purgatory, they were supposed to be simply "purified", that is, essentially reset – losing their memories and being sent back to being low-ranking, to work their way up to their former high positions.
Instead, however, Mark (who was an archangel) jumped in front of Ten (who was the chief of hell) into the water/goo/whatever that was meant for Ten, and would therefore purify him into a normal, low-ranking DEMON. Mark does this because, while they had been imprisoned, Mark and Ten had joked about how "the punishment for an angel should be doing bad things, while the punishment for a demon would be doing good things." He wanted Ten to be a good guy, and kind of "sacrificed" himself with the burden(?) of being a demon so that Ten could be the angel instead.
This pissed of Ten, and he tried to go after Mark, but heaven (the ones overseeing this whole operation) couldn't have the BOTH of them be reborn as demons... they had a balance to maintain. So, they kind of just accepted the fact they'd have to use Ten as an angel, and pushed him to be angel purification thing instead. But as he was being dragged to be purified, Ten made himself troublesome, which annoyed heaven and made them "punish" him with 100 years in the purification goo – meanwhile Mark would be in and out pretty quickly.
That's why when we begin the manga Ten is said to be a new angel while Mark is already a Duke of hell – he's been here for 100 years already, during which Ten was submerged in the purification water and just recently came out.
Therefore, the SWITCH was an accident. They were just supposed to lose their memories and begin as a fresh demon and angel – and, one day, assume their previous roles of chief of hell and archangel. Since the destroying of purgatory had been a result of a personal conflict between the two, this was meant avoid having them clash again in the future (since they wouldn't remember eachother).
who is ten why was he the demon and who is mark why was he the archangel??? did they switch or summ??