- The blue page is stapled to the red page.
In particular, would it be wrong to label "stapled" as past-tense in the above sentence?
Well, let's look at this a bit. First of all, your example sentence has only one tensed verb, and that is the verb "is" -- the verb "is" is present tense. There is no verb in your example sentence that is past tense.
The word "stapled" is either a past-participle form of a verb in a passive-voice construction, or it is an adjective in an active-voice construction, or the word could be ambiguous (where both possibilities of verb and adjective are acceptable).
I'm not sure how all interested you might be about this topic of "verbal passive versus adjectival passive", but that is a topic that can be rather lengthy and time consuming. I've already spent quite a bit of time on a recent lengthy post (about the pronoun "it"), so my fingers are a bit tired. But let me at least present to you some tidbits that could be used to support the idea that a passive interpretation for your example sentence could be reasonable.
(Note that no context for the example sentence was provided -- just an example sentence -- and so, that sorta means that we can create any reasonable context that we might want in order to support whatever it is that we're trying to prove.)
In general, if the "candidate" passive version has basically the same meaning as the active version, then that is usually good enough evidence to support the opinion that a passive interpretation is feasible.
And so, with that in mind: Imagine that we got a page of instructions. Those instructions could say something like,
"Customer staples A to B. Customer then staples C to D."
Those above instructions are in present-tense and in active-voice. Let's see what the candidate passive-voice version would look like,
"A is stapled to B. Then C is stapled to D."
Basically, that version has the same meaning as the active version (except that the active's subject info of "customer" is lost). This last version is also in present-tense, due to the verb "is". Here, the word "stapled" is a past-participle form of a verb, which is used in a passive construction.
And so, it seems that a passive construction interpretation -- where "stapled" is considered to be a past-participle form of a verb -- is reasonable.
(Aside: Passive constructions can also have an interpretation that has a stative meaning. That is, their interpretation is not required to have a dynamic meaning. But perhaps that topic is better for another day.)
In your example "The blue page is stapled to the red page": To compete with the passive construction (where "stapled" is a verb), it might be reasonable to consider an intransitive construction (where "stapled" is an adjective). In the intransitive construction, your example sentence might be a copular clause, where the word "stapled" is an adjective that has the function of predicative complement (and the predicand is the subject "the blue page"). Usually these types of constructions have an interpretation that describes a state.
But, what is important here is that, in both possible types of construction (passive and intransitive copular), the word "stapled" is NOT a past-tense verb form.
Hope this helps.