About joinig the league your league then changing to another one

Penalties - When leaving a league, firm penalties are applied to your team. The exact penalties will be listed before you complete the action for your consideration. This prevents league-hopping, and discourages leaving a league to help get your friend out of the relegation zone or other tricks.

As listed in the Rules and Regulations:

All players need to read the rules and regulations and the guide. There are many questions popping up in the forums that could be simply answered by reading those two pages located under the iGP tab.

As listed in the Rules and Regulations:

All players need to read the rules and regulations and the guide. There are many questions popping up in the forums that could be simply answered by reading those two pages located under the iGP tab.