Sometimes the best chemistry, is to simply PREVENT the chemistry of rust in the first place.
So in addition to the already well covered chemistry issues above, I think it's very important, that before coating the underlying surface, that that surface is both smooth and solid. Old guys refer to it being 'sound'.
So I've found that one important reason to ...
You can think about this problem from the definitions of surface energy.
The surface energy quantifies the disruption of inter-molecular bonds that occurs when a surface is created
The composition or structure of a surface depends on how the bulk crystal has been cut.
The electronic structure (or number of dangling bonds) depends on surface composition
If you plate the pieces with zinc or silver, the main source of zinc/silver in the ground coffee will be from abrasion between the parts and the coffee beans and not from chemical attack.
A few milligrams of zinc or silver (or iron for that matter) won't to do any harm to your health, specially if diluted in many coffee cups along several months or years.
Tritan is a co-polyester. It is prone to stress cracking in the presence of a number of common solvents - cyclohexanone and tetrahydrofuran are used as surface bonding agents.
Acetone can induce stress cracking, as can IPA.
I would suggest overprinting if you want to disguise the logo.
As for the aluminium item - take your choice - cyclo, THF, acetone, ...
I would suggest acetone for both - it's usually very effective for removing colours or inks of all kinds and I used to use it at work (in a lab - make sure you handle and dispose of it safely) to remove permanent marker.