If it looked like Dave Minehan wasn’t sure what the Replacements were going to play next during the band’s show at the Boston Calling music festival, that’s because he wasn’t. The former frontman of the Neighborhoods is wielding a guitar with the reconstituted Replacements these days, and he’s pleased to report the notoriously ramshackle rockers haven’t changed much. “It’s still a rickety roller coaster ride in a good way,” Minehan said of the ’Mats and mercurial singer Paul Westerberg. “You feel like you might fall out of the front seat.” Minehan said there was a set list for Sunday’s show, but, well, not really. “It only exists for the first four or five songs,” said Minehan, who also runs Woolly Mammoth Sound in Waltham. “I have to watch Paul and Tommy [ Stinson ] like a hawk because the minute I don’t, I’m gonna miss a cue. It’s like playing chicken with a real knife.” He said it was fun but also nerve-racking to play for the home crowd. “It’s wonderful, but, oh my God, the pressure builds.” (Local rockers Mike Gent, Evan Dando, Juliana Hatfield, and Peter Wolf were just a few of the folks who stopped backstage to say hello.) Tuesday, the Replacements will perform on “The Tonight Show Starring Jimmy Fallon,” which is surprising considering that Lorne Michael, producer of “The Tonight Show,” once banned the ’Mats after a shambolic (and profane) performance on “SNL” in 1986. Rolling Stones guitarist Keith Richards is also booked on “The Tonight Show” Tuesday, raising the possibility that Richards might join the Replacements for a song. “Boy, wouldn’t that be nice,” said Minehan.