Hey Alejandro,

Yes, you can do this with a custom event. I would advise using a JSON instead of hundreds of individual attributes.
There is a brief tutorial on how to do this available here -> https://docs.gamesparks.com/getting-started/using-cloud-code/
And you can see how this applies to Unity here -> https://docs.gamesparks.com/getting-started/using-cloud-code/unity-cloud-code.html

The size of the data depends. There is a limit to size of a request you can send you can see here  -> https://docs.gamesparks.com/documentation/key-concepts/system-limits.html
If you can tell us what kind of data you are sending we can advise further.

Thanks,
Sean