MLS expert please help ?

I play FM since 2006 but this is first time wanna try manage MLS team but not understand certain things. Anyone with knowledge please help

1 ) What is designated player ? How to get it ?

2 ) Why some player have GA ( Generation Adidas ) information ? What does it means ?

3 ) Why every team have different designated player and international ? Can it change ?

4 ) Why I can only click change button once ( at the bottom of team screen )

I already go to MLS thread but can't understand. Can you please answer my question even 1 or share anything about MLS that so unique

Thank You

1.) A designated player is 1 player that you get to have on your team that you can pay however much you want to but he only counts 400k per annum against your cap. Each team has 1 slot with the exception of teams who have traded their slots. Examples of Designated Players are Beckham, Juan Pablo Angel, Guillermo Barros Schletto, etc.

2.) Generation Adidas is a special designation for exceptional youth. They don't count against your cap and are basically gifted youngsters. They're useful.

3.) The reason they have different amounts of designated player and international slots is due to trade. In the MLS you can trade players, allocation money, draft picks, international slots, and designated player slots(up to 2). Basically, trade your player to another team in MLS for an International slot for 2 years and you will be able to sign 1 more international player than normal for the next 2 years.

4.) No idea why that's the case. Haven't had a problem with that. Maybe continue a bit then try again?