Can I spray flat enamel over top of my acrylic paint job without ruining my paint job ?

So long as you allow the acrylic paint to completely dry. Let it dry at the very least a week. Of course the longer the better.
If the acrylic paint has not fully cured, adverse effects could happen with the enamel.

Howdy whiterook,

BTW...Queen's bishop to......nah,never mind.

Please allow me to ask a question to you....why are you wanting to spray enamel over acrylic?
I can only assume you are trying to 'flat coat' over your base???
If this question is 'rhetorical', then my suggestion is to not spray enamel over acrylic.
Now....if you want to go the other way.......

Tread.

Been spraying enamels over acrylics, and acrylics over enamels for years, never had a problem either way. Just have to WAIT for the paint to completely dry, cure, what ever you want to call it.
If you can smell it, it ain't dry. If you can smell it it ain't cured.

to throw a spanner in the works my rule is...

enamels over acrylics anytime as long as the bottom coat is dry.

ONLY put light acrylic washes over enamel.

Thanks everyone.

Glenn,
I guess that you got the "completely dry" part. If you don't have all the time in the world, use a hairdryer to expedite the drying process. I have used my wife's hairdryer for years and it has always accelerated the drying time one hundred fold. Besides, I have used both ways and never had a problem (so far.)