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• Agnes Jurati - assimilated by the Borg in Fly Me to the Moon
• Kore Soong (and androids)
• Narek
• Raffi Musiker
• Chris Rios
• Elnor
• Laris
• Tallinn
• Adam Soong

• Agnes Jurati - assimilated by the Borg in Fly Me to the Moon
• Kore Soong (and androids)
• Narek
• Raffi Musiker
• Chris Rios
• Elnor
• Laris
• Tallinn - disguised as a Human in Farewell
• Adam Soong

• Benjamin Sisko - disguised as a Klingon in Apocalypse Rising
• Odo - almost always when not in the Great Link
• Jadzia Dax - disguised as a human in Trials_and_Tribble-ations
• Jake Sisko
• Miles O'Brien - disguised as a Klingon in Apocalypse Rising
• Quark
• Julian Bashir
• Kira Nerys - disguised as a Cardassian in Second Skin
• Ezri Dax

• Benjamin Sisko - disguised as a Klingon in Apocalypse Rising
• Odo - almost always when not in the Great Link
• Jadzia Dax - disguised as a human in Trials and Tribble-ations
• Jake Sisko
• Miles O'Brien - disguised as a Klingon in Apocalypse Rising
• Quark
• Julian Bashir
• Kira Nerys - disguised as a Cardassian in Second Skin
• Ezri Dax

Those in bold have never been visually transformed into another species on screen.

  Only one example is given to discount people.

• Jean-Luc Picard - disguised as a Romulan in Unification
• William Riker - disguised as a Mintakan in Who Watches The Watchers
• Geordi La Forge - transformed into Tarchanne in Identity Crisis
• Tasha Yar - half-Romulan daughter in Redemption
• Worf - disguised as a Boraalan in Homeward
• Beverly Crusher - transformed into a dog in True Q
• Deanna Troi - disguised as a Romulan in Face of the Enemy
• Data - disguised as a Romulan in Unification
• Wesley Crusher

Those in bold have never been visually transformed into another species on screen. Only one example is given to discount people.

• Jean-Luc Picard - disguised as a Romulan in Unification
• William Riker - disguised as a Mintakan in Who Watches The Watchers
• Geordi La Forge - transformed into Tarchanne in Identity Crisis
• Tasha Yar^* - half-Romulan daughter in Redemption
• Worf - disguised as a Boraalan in Homeward
• Beverly Crusher - transformed into a dog in True Q
• Deanna Troi - disguised as a Romulan in Face of the Enemy
• Data - disguised as a Romulan in Unification
• Wesley Crusher

^* counts by the question's clarifications, but I disagree