How to spin off module D1

Module D1 starts with mandatory Drow outpost hex D3. This is Map II, a generic corridor with some caves off its side. The DM and players' maps each orient that passage as leading in, southeast; and out, northwest. More: D1 has that overall hex as an intersection - northeast, for one, goes to O10. As part of the D-series map, the encounter sticks Map II immediately southeast. Let's add to the D3 hex, so the drow there can do commerce with other passages from that.

A hex is a mile-diameter circle, mathematically; plenty of room for a small side-cavern to the intersection. So, whatever feeds O10 can be similarly-distant to its northeast.

The least you do here is remove at least two F3 and one F4 Aleval males from the main encounter, nerf the former couple down to F2, put them in charge of whatever mixed-patrol beasties, and shift them to the northeast. The trio sets up an ambush at the intersection after the party has dealt with their Despana-led fellows. DMs over a stronger party can do more.

I'm leading to O10 which - narratively - goes to the great ghoul pantry ST17. One obvious thought for the mixed patrol: four ghasts with their 7-12 ghouls. Ghouls here are unfortunately (for them) led by ghasts who can be sniffed out near-literally a mile off. A Mixed Patrol may have some means to quell that until needed. I'd not use the True Ghouls from Wolfgang Baur's Dungeon #70 classic. (Not yet...)

Either way, along with the Mixed Patrol northeast: add humanoid captives. If the Drow cared for hostages they should lead them to the Vault personally; O10 gets mere slaves - or food. The captives are in various stages of paralysis excepting elves. (Elves are considered immune to ghoul paralysis by D-series rules.)

Good news for design: these three drow don't have to lead ghouls. Bugbears will get the job done. I insist that party own a players-map to O1, even unto ST17. Maybe R9 also. Icons seem clear: cow/mushroom for R9, three-link chain for O10, skull for ST17.

So, recommend D1's northeast spinoff be a drow-led bugbear mixed patrol with slaves. Vials of paralysis-potion/-poison, and cures for same. Hypodermic needles. These vials give off Evil on detection, and undeath; are made from ghoul toxin.