Episode I would be set in 37 BBY. As the Galactic Civil War was in the OT, the Clone Wars would be introduced in medias res. At this late stage, the Clone Wars is primarily between the Republic and Mandalorian Death Watch, a terrorist faction which rose to power after displacing the previous pacifist government on Mandalore, but the wars began as localized skirmishes between revolutionary syndicalist movements and corporations utilizing clone slave labour which snowballed into multiple large-scale conflicts.
The Jedi would be portrayed much like they are in the PT, except they’d be endogamous rather than celibate and wield only blue lightsabers. Knights would wear uniforms similar to Luke’s ROTJ outfit, while masters would wear uniforms closer to his TFA outfit; in both cases, the colour scheme would be black-&-gray rather than pure black or white.
Yoda would be absent, mentioned but not seen. A holdover from a time when the Jedi were more theologically liberal, his heterodox beliefs placed him in conflict with the Jedi Council, leading to his expulsion.
Obi-Wan would get Anakin’s backstory from the PT. Born Ben Lars, he would’ve grown up a slave on Tatooine with his mother and brother, Owen, until Yoda came to the planet and paid for their freedom when Ben was nine. Like Yoda, he’d be a maverick at odds with the Council.
Anakin would be older, around the same age Luke was in SW. Like Obi-Wan, he’d hail from Tatooine, but wouldn’t have been a slave. Rather, he and his twin sister, Beru, would’ve grown up together on the Skywalker moisture farm. Unlike Beru, who was content on the farm, he left Tatooine seeking a more adventurous life, becoming navigator on the spice freighter Twilight. A Han Solo type, he’d be completely uninterested in getting involved in the Clone Wars until meeting Obi-Wan.
The Padme Amidala character would be completely reimagined as Amidala Naberrie AKA Naberrie 38. The 37th clone in the Naberrie line which has served the Alderaan Royal House as personal bodyguards for generations, a quirk of fate made her Force-sensitive, unlike her predecessors.
Naboo would become Alderaan. Enlisting the aid of the native Gungans, the Mandalorians would invade the planet, seeking to procure the Alderaanians’ advanced cloning techniques. This would enable them to create longer lasting clone shock troopers.
Qui-Gon and Dooku would be fused into a single character. Another student of Yoda and an influential Jedi master in his own right, he, too, would’ve been expelled from the Order for his dissenting beliefs. Plagued by visions of a new Sith Empire rising from the ashes of the Republic, he’d reluctantly join forces with the Mandalorians, delving into forbidden teachings in a bid to destroy the Sith with their own arts.
Asajj Ventress would take Darth Maul’s place. Qui-Gon’s foremost apprentice, she’d have a pair of violet lightsabers.
At the end of Ep. II, Anakin would leave Obi-Wan and join Qui-Gon.
Palpatine would be fused with Darth Bane. Rather than establishing the Rule of Two, he’d have established the Rule of One; learning soul transference, he attained immortality by commandeering the bodies of his so-called apprentices, ensuring the Sith way would live on indefinitely, but only through him. Palpatine is only his latest host body.
Ep. III would end with the Jedi Council pledging their allegiance to Palpatine, with dissenting Jedi like Obi-Wan going underground. Anakin falling into a molten pit, the Great Jedi Purge, etc. would all occur between the two trilogies.
Only Qui-Gon and Palpatine would display telekinetic abilities. Other Force users would only demonstrate the subtle Force abilities depicted in ANH.
Not a single red lightsaber. Well, maybe in a vision, but that’s the extent of it.