i know this has been asked millions of times but is tuning guitar down to drop d and drop d flat bad for neck.

I usually tune it to these then when finished put it back to standard.
It will have no effect. Tuning down to drop c, drop b, etc you'll have to setup the guitar.
Jackson DK2M
Jackson DXMGT
Jackson Rhoads V
Jackson Stealth
Yahmaha El-Cheapo Acoustic

Randall G2
Randall Cyclone
Behringer 4x12 Cab

Dunlop Crybaby Wah
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Electro-Harmonix Metal Muff
ISP Decimator