As long as they are registered to play then all is legal.
The fact they also won doesn't bode well for the opposition!??
The following is from the MPL 2015 regs as provided to MPL at the start of the season.
Each Club has a wider responsibility to the code and the sponsers and to the supporters. this is achieve by providing and maintaining football of the best achievable standard, a well presented playing surface and first class facilities.
So maybe debatable if Coastal complied to this or not.
Standing on the sidelines yesterday watching the game I was left shaking my head on this 'planned' sub late on the game considering all the praise coming out of the club in the latter part of the week saying what a good job Xavier had done in his two years in charge and the great work GT has done at his time at the club to make it what it is today.
What next giving a sponser the odd cameo run during a game. .