They dont take over the tunnel... If you mean in Goldenrod. ;)
talk to a man in goldenrod tunnel, he will ask to take a picture. if you mean during the story, talk to a team rocket member in goldenrod tunnel, he will let you wear it.
By going into the Goldenrod Tunnel and going to the Team Rocket Grunt and then he will put you in a Team Rocket Costume.
Goldenrod's Tunnel
One you cant keep the outfit. Two its in the underground tunnel in goldenrod city. And three you get to take a picture with your Pokemon party wearing the outfit.
the underground tunnel in goldenrod
Go to the Underground Tunnel in Goldenrod City. There is a Team Rocket Grunt there who will give you a uniform.
defeat petrel if team rocket has taken over. he is in the chairmans room. he has a wheezing and 5 koffings. if team rocket hasn't taken over yet, go on with the storyline.
Fight them
you have to go back to where the photographer in the underground tunnel is and a team rocket grunt shall give it for you to wear
That's because in Gold Team Rocket do not take over the Game Corner. Instead they take over the Radio Tower.
You get it when they take over the radio tower in goldenrod city one of team rocket members gives it to you
Easy! Goldenrod Tunnel, in the north west of Goldenrod City.