on my 98 CX, the pillar mount antenna has one cable from the antenna
into the car, near the fusebox. then an extension goes from near the
fusebox to the radio.

i pulled the antenna out, cut the cable, then tightly duct taped the new
cable end to what was left of the old. pulled off the underdash knee
bolster cover(2 screws), unplugged from the extension near the fusebox,
and pulled the old cable out the bottom until the new cable was visible.

plug in, screw antenna base down, replace bolster cover. done.

no dash removal needed. honda wouldnt design something that way.

I did this on my 91 Civic.

You can buy a perfectly good new antenna at Pep Boys. OEM is
not essential, IMO.

Routing the antenna's wire is a little tricky. I bought some
10 AWG copper wire (with bright pink sheathing) at Lowe's or
Home Depot. It is the right stiffness for the job. I stuffed
the 10 AWG copper wire down the antenna orifice in the car
roof until I could see the pink on the left side of the
driver footwell. A bunch of wires are down there, so ideally
you'll have a helper who can wiggle on the 10 AWG copper
wire while you watch for it in the footwell. I think I then
put a loop in the 10 AWG copper wire and dragged the antenna
wire down.