Musing: Congruence blocking blocking, feasible?

Some introspection on me speaking Finnish recently got me thinking about things blocking congruence blocks. First, a description of the situation in Finnish:

Finnish negation works slightly like English negation - you have a negative auxiliary (ei, c.f. don't) which has congruence for person (en, et, ei, emme, ette, eivät, c.f. don't, doesn't, isn't, ain't, aren't, ... ). However, unlike in English, it does not take the infinitive, but a special form (the conegative form, which in the present tense indicative mood, for all persons is identical to the third person singular imperative), and unlike in English, tense, aspect and mood does not go on the negative auxiliary. Instead, the form the main verb takes indicates all this information. In the imperative, there's a special auxiliary (älä, älkää, älköön, älkäämme, älkööt), which in somewhat archaic language actually distinguishes a sub-mood by a special form (ällös).

Now, the thing that got me thinking is that as a semi-native speaker of Finnish, I have internalized these rules very well, but only so much that I sometimes get the feeling that deviating from them would feel more natural. Especially when the verb is emphasized, it feels like the usual verb form would attract more attention to it and the regular negation structure feels too mundane?

On the other hand, since the content verb has a very weakened congruence in the negative (in the past tense and in the imperatives, number is distinguished), one could basically argue that the negation serves as a congruence block. Is it reasonable to assume languages can have a block operating on a block this way?

I find the Finnish negative a fun thing in how non-natives sometimes deal with it: a fair number of Swedish-speakers maintain congruence and can even use the wrong verb form, so 'I didn't watch it' comes out as *en katsoin sitä (instead of en katsonut sitä)- where katsoin is the regular past tense indicative, and 'I don't watch it' comes out as *en katson sitä, instead of en katso s:itä. Estonian has a similar negative verb as Finnish has, but it lacks person congruence on it, and some Estonian speakers of Finnish carry that over too. During my stint at a place with lots of Estonian workers, I recall some of them sometimes going all pro-drop on negative sentences, thus obtaining wonderfully unclear statements like 'ei tiedä'. So, two relatively large groups of non-native Finnish speakers (I surmise there's more Russians than Estonians in that category, though) have quite the opposite mistake in their formation of the negative - one keeping too much information, the other omitting too much.

Somehow, I find the Estonian approach more likely to cause a congruence block block to appear, though.