Vintage Fender Guitar necks(and vintage-Style re-issues) having the truss rod access at the bottom doesn't necessarelly mean
remove the strings
un-bolt the neck
adjust
put back the string
measure
if not 100% start all over again lolol
the way u do it
is to detune the strings and turn the truss rod from where it is.
Most of the time u only need to turn just a little But i must suggest have a Professional luthier do this( he or she knows and does a better job than us)
for Strings a Jaguar is more of a Heavy strings type of guitar.
Like My American Vintage '65 Fender Jaguar ...in the store they Strung it up with 10s
when i got home in the nice-case it came with, Fender included a set of Flatwound 11s with a wound G string
I Checked with a Digital tuner plugin(Brainworkx Bx_Tuner) i realized alot of notes on the fretboard were out of tune
the store probably changed the heavy gauge for a lighter one without doing a proper steup job
being a Strat owner as well i find it better to have the Jack hole on the side
i'm no guitar maker but back in 1965 it probably meant a little more effort and in order to keep cost down they cut that corner(lol pun)