What mod or mods voids the warranty?

I have a 2009 SR5, TRD Sport, access cab Tacoma, V-6, 6 speed manual, I have had this rig since about a month ago and love this truck.

What mods can be done and not void the warranty?

 

I think you can do what ever you want, but if something wears out and they investigate it and determine the mod caused it then they will not warranty it.

 

The manufacturer must prove that aftermarket modifications, parts, or labor were the proximate cause of a failure for the warranty to be denied.

The manufacturer is not liable for warranty repairs on aftermarket parts or labor.

There is no such thing as "voiding" your warranty (extended service plans are a whole separate issue and MAY be voided subject to the terms outlined in the fine print).
If you replace your air filter with a CAI, Toyota may be able to void your engine warranty if they can show (and it's easy to do) that the CAI allowed more dirt to enter the engine, but if your transmission blows, they can not use the CAI as an excuse to avoid repair.

However, larger tires without corrective regearing may be used as a reason to void the trans warranty.