Don't do X. Уж тем более теперь.
While I understand the meaning of the entire phrase...
What is the function of "уж" here? And is it impossible to say "уже тем более теперь" instead?
Is "тем" the dative or instrumental case of "тот"? I suppose the same case applies to the "тем" in "тем не менее".
A) Here Уж is a particle of intensification, it can be dropped but at the expense of the phrase becoming somewhat dry and terse. In this sentence it can't really be replaced with уже. One can say тем более уже теперь but it's not quite the same in terms of expressiveness.
Although in some other cases they can be interchangeable, perhaps because in those уж is simply a short form of уже
Не виделись уж(е) несколько лет.
Ожидать уж(е) пятнадцать минут.
Не спать уж(е) вторые сутки.
Пить уж(е) третий стакан.
Уж(е) пятый раз приходит к кому-л.
In these examples уж sounds archaic and poetic (abbreviation of words for the sake of metre was one of poetic devices in the past) and isn't typical to modern language.
In the examples above the main form is уже and уж is its optional variant.
In yet other cases where уж is the main form it can be replaced with уже in different syntactical position (something that was already attempted above with inferior result)
Уж если я чего решил, то выполню обязательно = Если я чего уже решил, ...
Вот уж где действительно можно отдохнуть = Вот где уже действительно...
Уж чем наградил Господь, тому и радоваться надо = Чем уже наградил Господь, ...
И что уж я только ни делал? = И что я уже только...
The flow of these variant sentences isn't always smooth and there could be some awkwardness to them so they may not always be adequate as replacements.
B) тем is Instrumental not of тот but of то (their forms in 4.5 out of 5 oblique cases are homophonic) because neuter prepositions (то, оно) are typically used to point at abstract phenomena or phenomena in general.
This phrase would work without the "уж" particle; here it rather serves as an rhetorical embellishment, than an actual strengthening of the statement. Without "уж" the original phrase could be translated as: "Don't do X. More so (don't do it) now". With it: "Don't do X. Even more so (don't do it) now".
Don't mix "уж" and "уже". The first one is a grammar particle and not a word proper, it doesn't convey facts, but more like personal opinion of the speaker. The latter, however, is a proper word with clear meaning of passing some threshold/mark (usually in time, but sometimes in some kind of a row)
"Уж" is a modal particle, i.e. it gives an emotional opinion of the speaker. The exact meaning might vary greatly, but usually is something about annoyance of the speaker caused by inability of the other party to grasp a very simple idea.
In this particular case I tentatively translate it as "and it is your fault, you moron, that it is a very bad idea to do X now, and you should see it easy enough", but I need more context to be sure.
some random paper about the particle: link . If you can read it, it should give you an idea.
Partial answer.
Or maybe not even an answer but some related observations: as I was laying out examples, which I hope would clarify usage patterns, I actually instead got more and more confused myself.
And is it impossible to say "уже тем более теперь" instead?
In this context "ужЕ" would be synonymous to "теперь". Both words would mean that as the time went by the situation at hands changed and what appeared feasible earlier is no more.
Because of this "уже тем более теперь" would be a mistake like "Чёрная кошка перебежала дорогу чёрная". A bit too many.
Compare with possible phrase "уже нельзя". That is how "уже" would get parsed in that phrase.
Now, can you say "уже тем более" without "теперь" ? No, again. As "уже" indeed has a function of amplification, and lacking "теперь" would get bound to "тем более". But you can not amplify "тем более".
However you can bring both "уже" and "теперь" words together.
"Теперь уже тем более [не стOит так делать]" or "Сегодня уже тем более" or "Сейчас уже тем более". In those examples while "уже" still seems synonymous - it is not redundant. Instead it is amplification by repetition. Kind of "черный-черный кот" pattern in a remote sense.
Now one extra brush stroke. "Уже теперь" vs "теперь уже". In some vague sense one refers to the past and another to the future. Or perhaps it is positive/negative sentences that make difference.
vs
Or, with "теперь" omitted, a simpler phrase
Or if TV discusses some prospects of having good crops.
vs
Frankly, I can feel those intonations differences, but I can not rationally explain them and fail to word some clear rules.
