Remove the airbox (like you would to change the air filter), and maybe remove the lower air duct as well (I can't remember) and you will have plenty of room to change these lines directly from above. Just remove the 2 clamps at the trans, and the 2 clamps at the radiator, and replace the hoses.
If you also have the inline aux transmission cooler, then you will have 3 rubber lines:
I can't remember what the flow-direction is, but be sure not to reverse anything. Mark them if necessary.
If the line you need to change is one of the lines that go to or from the aux cooler, then the job may be more involved. All bumpers are not created equal, but on my '00 G.Voyager, I was able to remove the grille without pulling the entire bumper. Start by simply removing the 4-6 bolts you see holding the upper bumper/grille to the radiator-mounts. This should allow you to pull the top of the grille/bumper away from the radiator and get some access. You will then see that the bottom of the grill is held to the bumper with 5-7 push clips. You may need a flat-blade screwdriver to pry them lose, but try not to bend them. PS - Mine was only held with 3-4 of those tabs, but it's very secure anyway.
But before you pull the grille off, if you don't think that will help you, don't bother. In that case, just remove the bumper/grille as an assembly. You have about 8 push pins underneath. Then remove the front splash shields in the wheel wells, and find 1-2 bolts on each side holding the bumper ends. The bolts are probably the toughest part, as they are well-hidden. With the bumper removed, everything is exposed.
This all sounds very involved, but you can have the bumper off within 30 minutes.
2000 Chrysler Grand Voyager SE (3.3L Flex Fuel "G")
Purchased January 2008 @ 80,000 miles
Options: 2nd row buckets, rear A/C
Mods: Full upgrade to 8-speaker Infinity audio; hitch, wiring, brake controller, sway controller, & WDH kit for towing 3000 lb popup camper
R&R: 1 front & 1 rear hub/bearing, front sway bar bushings & endlinks, 1 outer tierod end, trans-shift solenoid pack, main & aux/rear A/C condensers