James Brown's second-half strike was enough to consign the Gills to a third consecutive defeat.
"There will be changes on Tuesday, but it is not just down to this game. (Goalkeeper) Simon Royce was always going to play no matter what," said Stimson.
"We want to beat Blackburn and after this performance there may be more changes than I first thought.
"Places are now up for grabs. We have lost three games on the trot and you can't get away from that. So if whoever comes in can show they have got that spark, the shirt could be theirs.
"There's only one person who has possibly guaranteed his shirt for next week's game against Walsall and that's probably Jack Payne."