What if you are using a design plan exactly with the same diameter
material but with different material, say conduit instead of copper?

I would expect that the tuning would not change appreciably. The
antenna's losses might be higher, but likely not enough to be
noticeable.

If you direct connect an so connector. How do you adjust both sides? I
mean once the ground is in place it is hard to adjust the "hot" side
unless you bend the wire alot.

You experiment a lot.

Maybe you build a bunch of antennas with different attachment points,
and measure them out. Or, maybe you cut one copper-pipe J-pole,
don't actually solder the pipes together yet (just depend on a
friction fit while tuning), drill a spiral pattern of holes or a line
of holes in the pipe to which you can try screwing the SO-239, and try
a bunch of positions until you find one which works best. You then
rebuild the antenna with a new piece of pipe which is drilled for the
socket in only one place.

Or, you build a mounting-and-grounding bracket arrangement which
allows easy tuning... as is shown very clearly in one of the two sets
of plans I referred you to in the post you're replying to.

Like I said, the easiest way to get a working antenna is to exactly
reproduce a known-working example. If you want to vary the design,
you'll need to experiment, cut-and-try, and be willing to make
mistakes and learn from them.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!