Paul's chance to set the tone
Marhshall oping to disrupt the natural order
"If you are on the bench, your mind-set can be different depending on how the game has gone," Marshall explains, and he is well placed to outline this scenario.
"Sometimes it (the game) is already won and you're trying to rack up the pace and score a couple of extra tries. For others it's very tight and you are trying to play more tactically and put pressure on the opposition.
"So you're not playing on the hoof because you have time to think and you have to be thinking of playing in different zones so it's a bit trickier than starting where you get the feel for the game," the 28-year-old says before bringing in a more personal observation.
"Something I have learned over the last few years is that if you try too hard it doesn't work.
"You have just got to play like you play each week, if you try to force things more often than not it doesn't come off so you just have to play your own game," he says.
Even so, it is still a tricky enough balancing act for Marshall who is closing in on his 120th Ulster appearance.
But tonight he gets a chance to start at scrum-half while Pienaar is benched and, as such, should get that all-important feel for the game from the off.
He will also link-up with Paddy Jackson again, a half-back combination that was last seen in late November's PRO12 game at Zebre, just prior to the back-to-back Heineken Cup clashes with Treviso and allows Marshall to feature alongside a player whose form and influence is clearly on the rise.
"I think he is a smashing player and he has had a great season so far," says Marshall, rightly singing Jackson's praises.
"He has matured massively over the last 18 months and he is knocking on the door of the Irish team.
"He is very composed and I like playing with him," says Marshall, which seems like a timely moment to discuss his own hopes of further national recognition which are not in quite such rude health as Jackson's appear to be – Marshall won his third cap, all have been off the bench, against Canada last June just months after his first was finally secured in Ireland's Six Nations defeat to Italy.
"To be honest I think I'm a bit down the pecking order at the minute and I don't think I can look too far ahead as regards that," he says.
"I've just got to try and keep playing well and if I am playing well I'll be happy and if anything else comes from that brilliant," Marshall says before adding an assessment of where he is currently at with his game.
"I maybe haven't set the world alight this year but I don't think I have played badly and maybe I haven't had some of the highlights I've had over the last year or two which can sometimes get your name mentioned and get you attention.
"But I've been steady enough and if I can put in a few solid performances over the next few weeks you never know, there are a few guys ahead of me but it is something to keep working on," he says, probably knowing that his best hope is to be involved with the forthcoming Wolfhounds game with the England Saxons at the end of January.
As for tonight's challenge, Marshall readily accepts that Ulster's record in Dublin is hardly the stuff of great encouragement but then there is that win last March to help nourish hopes and focus minds.
"It was a great performance down there last year to win," he says of the first PRO12 regulation season win in Dublin since the year that Ulster lifted the European Cup, "but we were disappointed with how the (PRO12) final went last May but (going to the RDS) doesn't hold any fear for us.
"I think when we turn up and play well we can beat any team in the league home or away.
But it comes down to our own mind-set. As you saw last week we were probably a wee bit off and didn't put Zebre away the way would have liked to but we know if we're in the right place mentally we'll be fine."
"We've had five wins on the bounce so we'll want to continue that," Marshall stated before looking at the bigger picture.
"It's a big few weeks and it doesn't get much bigger than Leinster and Munster and then rounds five and six of the Heineken, so it's an exciting time for everybody to be involved."
He knows, of course, that he is only likely to be starting for those vital European games if there are injuries to either Pienaar or Jackson.
So, tonight, at the RDS, he knows it is his chance and he must make the most of it and bring his trademark sharpness around the fringes to keep Leinster's close-in defence honest.
As has been the mantra all week, leading into the next two interprovincials, no-one will be found lacking in extra motivation.
"It's certainly competitive when the Irish provinces play against each other and when we play each other around Christmas there is always an added incentive to try and get one up on those guys," Marshall said.
Now it's Marshall's turn to set the tone, while Pienaar does the waiting for game-time.