Sure. This is done with landscaping quite often.
The transformer doesn't particularly care since it's just getting line power in... or not.

Wire this with dual power paths into transformer. Timer before photocell as one path. Then motion detector as the second path. You must use only one circuit for this and should have a master switch to turn it all off for service. If the lights are already on, detecting motion just sends the power again without any issue (when you use same circuit).

One of the lansscape lighting companies have or had a ready to go product that did this but I can't remember which.

Thanks for the responce fellas.
There will be just one 110v. circut with a on-off switch. I guess my concern is that if one control turns the system on then there will be feed back from the transformer to the other control. I had planned on using 'PRECISION' mod. ESC-124DS photo cell,it's the only one I could find with a timer, and they won't say if feed back is a problem. I have searched for a combo unit, with zero luck. So I'll go with the two path system you sugested and see what happens.

Thanks again