VTF and VTA- Constant or not?

Dougdeacon already covered the set-up details extensively, but let me add that the correct VTF in a given cartridge defines the correct position of the cantilever (= the coils in the magnetic field) towards the magnet(s) and that the correct SRA/VTA is always a matter of the position of the polished area of the stylus towards the grooved wall.
That means ultimately that the VTA/SRA has to be groove-compliant - its a direct result of the cutting angle of the respective record. So it should be set with each record independently.
Painstaking sometimes.

Back in the late 1980ies and early 1990ies the collectors of vintage original vinyl (most notably the RCA LSC, Mercury SR, DECCA SXL and HMV ASD and SAX series) from a loose "circle" (most of them US-based). These gentlemen (and one lady...) did fairly early discover that there is a certain "angle" with the cutting laces in the various record companies. So there was something like a "chart" - were you could literally read down the VTA settings for a SXL, LSC, SR, ASD etc.
It eased up things quite a bit. The relative settings always were the same - no matter whether you use a 9" or 12" tonearm - just the relative distances changed according to the effective length of the specific tonearm.
I do not want to go into detail with this, but I can give you the two cornerstones of the chart: - Ortofon/OPUS3 have the highest required setting - i.e. the tonearm almost horizontal. Mercury SR is the deepest. About 14 mm down with the tail with a 10" tonearm.
Everything else (read: all other record companies LPs between 1958 and 1984) fall between these two extremes.
Give it a try.

Dan, yes - horizontal level and from that point up to 14 mm down. With a 10" tonearm. Its slightly less with a 9" and a bit more (which isn'T possible with all cartridges/12" tonearms, since under certain conditions (small cartridge body, little height of cartridge body) the armtube touches the platter when you go that far down.
I mentioned this as a general "guideline" only.
Everyone will find his/her own "chart".
VTA on the fly makes this nor really a joy to find out, but eases things considerably. The change in effective length due to change of tonearm height is neglected here (never thought I would use the phrase ever regarding tonearm geometry ...) - it is too small to be corrected by hand at all. Much more important to the sound performance is to have the VTA groove-compliant.
And yes - some suspension do give in with age - some never.
My 28 year old FR-7fsp. still works with the very same VTF as in 1982. Fitted with its 5th stylus now, but same compliance. 80+ µm trackability with its lower limit optimum VTF set.
Certainly not the rule but maybe one of the very few exceptions in high-end cartridge history.
Cheers,
D.