Do I have a Frankenwatch

Based on the photo, yes this is now a frankenwatch.

Omega allows conversions of watches, but it must be a complete conversion from one model to another model where they both share the same movement. To the best of my knowledge, Omega never made a watch like the one you have now, with a black dial, Cal. 1151, and a silver polished bezel. So you have a mix of parts from different models, which is something Omega doesn't condone.

Cheers, Al

Sorry, but this is not correct. First, there is no movement number, as these movements typically didn't come with serial numbers. The 7750 based watches of this era only had serial numbers if they were COSC certified, and the 1151 was not.

On these watches the serial number is on the outside of the case back, and that serial number will coincide with a watch reference number. In this case it's a guess, but the watch likely started life as a ref. 35213000. It now has a case for that reference, a serial number for that reference, and a dial from a ref. 35205000. Dial doesn't match the serial number, reference number, or case number (35213000 and 35205000 have different vase numbers and case backs).

The first thing I do when I get a watch in, is check the serial number to see what reference it pulls up, and I'm quite sure Omega does the same. Even without doing that, as I've said that dial doesn't go with that case.

If taken to an Omega service center, they will likely tell the OP that it has to be changed back to what it was, and they will charge for the parts required to do that. Again that is the policy clearly stated in Omega's customer service documents. Of course policies don't always get followed, so there's a chance it might not happen, but if the service center is on the ball, they will want to convert it back.

Here is the relevant Omega policy...

"As a rule, OMEGA restores/reassembles all OMEGA watches to their original condition. If the movement is not of OMEGA manufacture, services will have to be refused.

OMEGA reserves the right to restore a watch to its original condition even after receipt of the approval of the estimate if, during the service process, the timepiece reveals not to be of origin. It will be decided on a case by case basis if the necessary work and components are offered free of charge or against payment. If against payment the customer will always be contacted before the work is carried out."

And yes, I've seen people on forums say that when they sent in their modded watch to a service center, Omega made them convert it back or they refused to service it.

As noted above, who pays is handled on a case by case basis, but my gut tells me this is going to be related to the costs. So for example if you send in say a 25318000 that has had sword hands installed on it, since Omega replaces hands at service anyway and it's included in the pricing already, they will just put the proper skeleton hands on the watch at no additional charge. If they have to replace something more costly, such as a dial that worth several hundred dollars as in this case, I doubt they are going to do that for free.

Now are there examples where people have sent in modded watches, and no one caught it? Yes I'm sure there are, but the policy is to bring the watch back to the factory spec. if possible.

Regarding what Rolex gets hammered for, the list is long...so this is probably on it, but at least Omega doesn't steal your parts as Rolex does.

Cheers, Al