PDF: Change 1 color on all pages?
Max Wyss has the best suggestion; using Acrobat's Print Production Tools.
Specifically you want to use the 'Convert Colors' Tool.
The key is the 'Conversion Attributes'.
Convert Command: Convert to Profile
Conversion Profile: (Choose from:) Dot Gain ??% or Gray Gamma ?.?
Rendering Intent: for a gray-scale conversion like this, I lean toward 'Perceptual', but it's not a strong preference.
You might want to check the 'preserve black' option. 
Test your settings with a small page range before doing the entire document.
So I have this 700 page pdf that's in black, white, and hot pink. The hot pink is both text and non-text (design elements). Is there any way to edit that one color on all the pages at once? I can do it element-by-element on adobe acrobat and page-by-page in photoshop, but those methods just seem impossibly tedious. 
I don't know much about coding but can maybe pull together something on python if I'm given great instructions. 
Thanks!