Stephan Elliott’s screen version of Noel Coward’s 1926 play is somewhat like Oliver Parker’s 2002 adaptation of Oscar Wilde’s “The Importance of Being Earnest.” The screenplay by Sheridan Jobbins hews to the general outline of the original but makes considerable changes in detail, and she and Elliott add substantial comic bits of business, many of near-sitcom character.

But while that sort of treatment was devastating in the case of “Earnest,” resulting in a movie that was less adaptation than bastardization, it’s much less offensive in this instance, and the reason is simple. “Earnest” is a masterpiece of such perfection that putting the slightest foot wrong in presenting it is a mortal sin. By contrast Coward’s “Easy Virtue” is a piece of singularly modest accomplishment, especially in comparison to his best work, like “Blithe Spirit.” (There’s a reason it’s so infrequently performed.) So changes to it aren’t nearly as objectionable. And while they don’t transform a sow’s ear into a silk purse, the liberties they take make for a slick period comedy-drama that older audiences in particular should find amusing.

Coward’s main point in writing “Virtue” was to excoriate British class snobbery, and that theme remains central here. But the tweaks are many in the Jobbins-Elliott reworking. The time is still the 1920s, but the heroine, Larita (Jessica Biel), is now an emancipated American woman who just happens to be a precedent-shattering automobile racer. She marries young English aristocrat John Whittaker (Ben Barnes) with the understanding that they’ll take a house in London. But when they visit the family homestead, his domineering mother (Kristin Scott Thomas) insists that they stay, and he’s too weak-willed to refuse. She’s also appalled that her son’s made such a terrible match; openly contemptuous of Larita, she aims to break up the couple posthaste. In this she’s helped by her two daughters (Kimberley Nixon and Katharine Parkinson). And there’s a local woman, Sarah (Charlotte Riley)—a long-time friend of John’s—whom she considers a far more suitable daughter-in-law.

But Mr. Whittaker (Colin Firth) has been transformed into a much more obvious ally to Larita, and given a detailed World War I background that explains the unlikely rebellious streak he plays out in extreme form in the end. And the Whittaker butler, Furber (Kris Marshall) has become far more of a co-conspirator, particularly in the matter of a little dog that’s the subject of a bit of Jobbins-inspired slapstick, which is a description one might also apply to an episode focusing on a local talent show, and to another about a fox hunt. When one gets to the last-act revelation concerning Larita’s first marriage, the details of a scandal in her past have also been rather significantly altered.

But most of the changes and additions Jobbins and Elliott have made to Coward’s text aren’t troublesome, as Parker’s were in “Earnest.” To the contrary, though they might be condemned by purists, they actually enliven a piece that could otherwise have seemed very stale indeed, even if they sometimes go a bit far.

Among the cast, Biel proves herself an adept comedienne as Larita, and Scott Thomas shows herself willing to play a smug snob to the hilt; Firth uses his hesitant manner nicely as Mr. Whittaker, and Barnes brings the right measure of youthful weakness and pomposity to his son. The secondary roles are well filled in a “Masterpiece Theatre” sort of way across the board, with the standout undoubtedly Marshall, who effortlessly wins chuckles as the servant with little respect for his employers.

As important as the actors is the luscious look of the picture. The British locations are lovely, and well caught in Martin Keene’s widescreen lensing, and the costumes by Charlotte Walker are period-right, as is John Beard’s production design, Mark Scruton’s art direction and Niamh Coulter’s set decoration. Marius de Vries’s score is pleasant enough, but it’s the insertion of songs by Coward and Cole Porter into the mix that captures the mood best.

It’s not easy to resuscitate a stiff, which is pretty much what Coward’s play is. But while everyone won’t agree with the approach taken by Jobbins and Elliott, it does result in the sort of mildly amusing, feel-good period piece with an easy-to-swallow message that appeals to today’s older audiences.