Can -Hom and -'a' be placed on any noun?
I've noticed than in most text I've seen, these particular suffixes can only be applied to certain nouns, to create new ones which also have a direct English translation, such as vengHom or vaS'a'. I've only ever seen one exception to this: one of the lyrics in the song "Duj Tivoq Tah" (sic) by Kosmic Horror, is yIHHommey, which wouldn't have any English translation I can think of, despite that I understand the idea of it. Is this a valid way to apply this suffix? Does it follow that (almost) all nouns and be modified in this way?
Theoretically they can be applied to any noun. Whether it always makes sense or not is a different question. And certainly even many nouns that make sense won't have a convenient English single word definition. My favorite way to translate -Hom is "minor" and -'a' is "major". I have no idea what "minor tribbles" are, but I don't doubt that there is something in this universe that could be called that.
One of the games they like to play at the KLI is to pick a noun and try to figure out what it would mean with -Hom or -'a' added to it.
When you play this game, try to avoid the temptation to simply think of -Hom and -'a' as merely smaller and larger versions of the noun. There is usually a change in what the noun actually is. A qachHom isn't just a small building; it might be a shed, where the purpose is slightly different than with a standard building. A De'wI'Hom isn't just a small computer but might be a mobile computer.
Sometimes the -Hom version of an animal makes sense to be the juvenile offspring. If the noun is abstract, like ngoch the result could be something like an unofficial de facto policy, or a subparagraph that was part of a full policy. The only time I would say -Hom is forbidden is on a noun that already has an -oy or -'a' suffix, but in-the-know Klingonists will have already thought of an exception to that rule. As Jeremy uses "major" and "minor" I tend to use über- and -ette. They don't often make real English words, but usually the feel is something you can translate.