This is a very common misunderstanding in my view. The idea of restricting tense within a paragraph (as I've heard it) is intended to be a restriction in narrative for the sake of clarity, to show the reader when things were happening. If that's clear, then that "rule of style" certainly doesn't mean that ideas within the sentence can't be addressed in the appropriate tense.
This concept seems hard for many to articulate, and for some, hard to decode within text. My best explanation is to use the following examples:
I was sick yesterday, but today I am fine. I'm all better now.
Locally, the was is past tense, but I never shift the notional view of "speaking from now" - the present, as when I was writing. I was narrating past events from the present, then describing the present. I stay always in the "present".
He loaded a pistol. He cocked the hammer. He takes aim and he's firing his gun at me.
This breaks the rule. Firstly, it sounds like I've survived the attack and am writing about a past event. Then part way though it seems like it's happening now. Regarding style, much is written in this form of present tense (apparently) to give it greater impact on the reader and reduce 'psychic distance' - to get the reader more involved.
You can refer to past events, future, present, all in one paragraph - or sentence even, otherwise you couldn't express much in the English language at all. But the governing tense of the paragraph, or sentence, should not be mistaken as the tense of any individual word therein, but rather, recognised as the overall 'temporal position' in which the portion of narrative is given.
Hope that helps.