Mossie Lawlor comes in on the right wing for the injured John Kelly (ankle), as Gaffney's charges bid for a third win of the campaign.
"These home-and-away head-to-heads with Castres are massive matches for us," said Gaffney, who welcomes Castres' coaching duo Christophe Urios and Philippe Berot to Thomond Park on Saturday week for the return.
"But it is going to be tough, very tough. We know a fair bit about Castres, and they were certainly busy during the summer, recruiting in a big way.
"Castres are also going strong in the French Championship, and it is going to be extremely difficult for us on Friday," he added.25-year-old Lawlor's inclusion marks the only change from October's tight 20-18 win at the Ospreys. The backline is boosted by returning Ireland internationals Ronan O'Gara and Peter Stringer - the sole try scorer last time out in Wales.
O'Gara is just 18 points away from becoming the Heineken Cup's record points scorer, with Diego Dominguez his target on 645.
Anthony Horgan, who missed out on an Ireland start against the US Eagles last month, is back on the left wing after time out due to a hamstring strain.
Deputy fly-half Paul Burke has shaken off a neck injury sustained in the 11-0 Celtic League win in Edinburgh last weekend, to take his place on a replacements bench which includes hooker James Blaney.
Marcus Horan, Frankie Sheahan, John Hayes, locks Donncha O'Callaghan and Paul O'Connell, and skipper Anthony Foley are all back from international duty, with tighthead prop Hayes set for his fiftieth Cup appearance and a well-merited ERC Elite award.
Hayes will be the third Munster player to collect the accolade - 31-year-old Foley leads the way on 62 caps.
Munster's French hosts have named former Ulster prop Justin Fitzpatrick in their front row, and have opted for Xavier Sadourny at number 10, instead of Yann Delaigue.
(15) Christian Cullen(14) Mossie Lawlor(13) Shaun Payne(12) Rob Henderson(11) Anthony Horgan
Replacements:(16) James Blaney(17) Gordon McIlwham(18) Trevor Hogan(19) Alan Quinlan(20) Mike Prendergast(21) Paul Burke(22) Mike Mullins