Change one drum without changing the whole kit
Select the drum and choose Edit Drum. Now pitch, envelope, filter and the other pages only change that hit. Whole Kit takes you back to the shared settings. The Editing line shows which drum you’re changing.
Use it when the kick needs a shorter tail but the hats should stay as they are, or one hit needs a different tone.
For S9 Sampler 0.1.6 (paid beta). More help inside the app: Help & Shortcuts → Drum Kits.

Step by step
Select the drum
Click the drum, choose Edit Drum and check that the Editing line names the right drum.
Shape it
Make a small change to the envelope or tone, then play this drum and another to check that only one changed.
Use Whole Kit for shared changes
Switch to Whole Kit for changes every drum should get. A drum with its own settings keeps them.
Save
Save Kit keeps the whole edited kit. In a saved kit, Save Drum lets you Replace Original or Add Version for just this drum.
Good to know
Add Version adds a sound
A new version joins the kit, which can shift later keys. Check Key Map and your MIDI afterwards.
Save Drum saves one drum
Save Drum doesn’t save your Whole Kit changes. Use Save Kit for those.
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