(1) - function - yes
(2) - function - yes
(3) - function - NO - Data tag parsing failed

(1) ============================================================================================================================

blockdata -903 61 1012
{
  Text2:
  "{text:\"Click here to\",color:blue,
     clickEvent:
         {
             action:run_command,
             value:\"/execute @p ~ ~ ~ scoreboard teams join Player_01 @p[team=]\"
         }
  }",
   Text3:
  "{text:\"start game\",color:blue,
     clickEvent:
         {
             action:run_command,
             value:\"/execute @p[team=Player_01] ~ ~ ~ setblock -885 57 998 redstone_block\"
         }
  }",
   Text4:
   "{text:\"===============\",color:gray,
      clickEvent:
         {
             action:run_command,
             value:\"/execute @p ~ ~ ~ say TEST\"
         }
   }"
}

(2) ============================================================================================================================

blockdata -903 61 1012
{
  Text2:
  "{
    text:\"Game in progress\",
    color:red
  }",
  Text3:
  "{
     selector:@p,
     color:yellow
   }"
}

(3) ============================================================================================================================

blockdata -903 61 1012
{
  Text2:
  "{text:\"Click here to\",color:blue,
     clickEvent:
         {
             action:run_command,
             value:\"/execute @p ~ ~ ~ scoreboard teams join Player_01 @p[team=]\"
         }
  }",
   Text3:
  "{text:\"start game\",color:blue,
     clickEvent:
         {
             action:run_command,
             value:\"/execute @p[team=Player_01] ~ ~ ~ setblock -885 57 998 redstone_block\"
         }
  }",
   Text4:
   "{text:\"===============\",color:gray,
      clickEvent:
         {
             action:run_command,
             value:\"/execute @p ~ ~ ~ blockdata -903 61 1012
                     {
                         Text2:
                         "{
                             text:"\Game in progress"\,
                             color:red
                         }",
                         Text3:
                         "{
                             selector:@p,
                             color:yellow
                         }"
             }\"
         }
     }"
}