A tough-talking Thomas said several Saints' players had forfeited their right to be in the side for what will be the Saints' first final in Melbourne for six years - following last week's meek 80-point capitulation to Brisbane in the qualifying final at the Gabba.
And he has already nominated Stephen Milne, Stephen Powell, Sam Fisher and veteran Justin Peckett as the players who could force their way into the side, with Powell the most likely to return.
And while Thomas did not name those players who could lose their places in the side - those under pressure to stay in the side include Brent Guerra, Allan Murray and Xavier Clarke.
Thomas said there was no way the Saints could stick with the same side after last week's hiding in Brisbane.
"There are a few guys we are looking at very closely," he said on Tuesday as the Saints re-acquainted themselves with the MCG by training at a ground where they have played just twice (for two losses) this season.
"That's understandable given the size of the loss and the way we went about it."
"We need to make some changes in that regard."
"You only get one chance to represent this club with the level of dignity that is expected (in a final) and last week we were well off the mark so you relinquish your rights under those circumstances."
However Thomas said last week's mauling had not affected the players' confidence going into Friday night's knockout clash with the Swans - who inflicted the Saints' first defeat of the season when they clashed earlier in the year in round 11 at the SCG.
"We go into this game with a great deal of confidence," he said.
"But what we have got to do is make sure we hold our belief all the way through."
Thomas said he was not using any "magic tricks" to re-build his players' confidence after last week's devastating loss but called on them to remember what has worked so successfully for the club throughout much of the season.
"I haven’t got anything other than facts and honesty and really calling on the players' character and integrity - which has got them through 16 terrific wins this year and got them into top spot for 80 percent of the season."
