What do you mean ? Object 1 is an animation looping forever ?
Object 2 is an animation stopped at 0 sec, that plays only once when mouse rolls over it ?
Object 1 and 2 are the same animation => instances of the same symbol ?
Yes, object 1 is an animation looping forever and object 2 stopped and plays only when mouse rolls over it. Object 1 and 2 is the different symbols, but at the same animation project.
So, inside object 1's timeline, at the last timecode, you add a trigger (pseudo-track Actions) with action Play from :
Inside object 2's timeline, at timecode 0:000, you add a trigger with action Stop :
Finally, in the main timeline, you select element object2, then add an action, select a mouseover event, then a Play action :