1962 Constellation - Replace Crown?

I would say it depends on your habits. If you wear it every day and it remains wound with the rotor then I would have a watchmaker put on the original decagonal crown which gives it a better look. Like others said, I wouldn't be too sure about water resistance either way. If you wear it occasionally and will need to wind it and change the date each time, it may be better to keep the service crown which is probably going to be easier to turn than a decagonal crown. That has been my experience, anyway

True. Are any good modern versions of the decagonal crowns made or is there a reliance on the supply of original ones?

The original crown looks very nice. As others have said, curious that Omega didn't have such an iconic crown available. I concur that the service crown should be left on for the warranty period, then have the original restored...certainly will stay nice longer.

They do still make decagonal crowns, but not for this particular case. A solution that I've seen other watchmakers use is to mount a non original crown tube with 2.5 mm diameter and simply use a new decagonal crown for a different case (such as 069ST42019 I think). It's a little bit larger, but it still looks good and is very preferable to the standard replacement crown imo.