The Ibrox boss road-tested a 3-5-2 line-up during their pre-season work out and then gave the system its first competitive outing during the 2-1 extra-time win over Hibernian on Tuesday.
After starting brightly by taking the lead with Lewis Macleod's early strike, the Light Blues struggled to impose themselves during the Petrofac Training Cup first round tie.
That forced McCoist to switch back to 4-4-2 as he brought off defender Darren McGregor and replaced him with David Templeton with 23 minutes remaining of normal time.
The move paid off though as Templeton lured Leith goalscorer Danny Handling into a wild tackle that earned the striker a straight red card.
The extra man paid off for the League One champions as they eventually clinched victory with Law's extra-time strike - but the match-winner admits they are not yet comfortable with McCoist's game-plan.
He said: "It was a tough game. Hibs played really well. They put their system on the game more than we did, particularly in the second half.
"For 20-25 minutes we couldn't get near them.
"In the end we were just relieved to get through. There are things for us to work on and we will do. We will get better.
"We have been using this new 3-5-2 formation which we have tried out in a couple of behind-closed-doors games during pre-season.
"It has worked well during that spell and did again during the first half against Hibs. But after that their system dominated ours and we had to change.
"It is going to take time - if we are going to persist with this new shape it will take work."
Rangers have already travelled to the Highlands for a two-game tour, jetted across the Atlantic for a four-match jaunt to the US and travelled south last Saturday for a friendly clash with Derby.
Games with Fulham and Partick Thistle were also added to their schedule and Law admits he is already feeling the pace just one game into the new campaign.
"That is our 10th game already. We had nine games in pre-season so it has been a tough schedule," said the Englishman ahead of Sunday's Championship opener with Hearts.
"We have travelled 13,000 miles to play four games in America and then had a nine-hour coach journey down to Derby, where we had another tough game.
"We played with 10 men for the last 20 minutes and got the run-around, so the last thing we wanted against Hibs was to go to 120 minutes.
"But we showed character to come through it and the main thing is we are in the second round."
While the performance was lacklustre, the Light Blues did at least gain a mental edge by overcoming Alan Stubbs' side ahead of the forthcoming promotion race.
Rangers completed last season's League One campaign without defeat but former Motherwell midfielder Law claims the Ibrox men already know it will be much harder this time as they line-up on the start-line against the Edinburgh duo.
He said: "The manager said after the game that if we needed telling how hard it would be this season, we just got it there.
"We know it's going to be a lot, lot tougher than last season with Hibs and Hearts to face.
"It is an exciting league and Hibs were impressive against us. They passed the ball around well. They have dangerous young players who showed up well.
"But it's credit to ourselves that when we were struggling, the manager changed it and we swung the game back in our favour."