...but does anyone know how much it costs to get the tires unmounted/remounted? Like ballpark price so I know where to call around/what price to go with?
Ballpark for unmounting/remounting/balancing tires is ~$20/corner. My local alignment guy will do it for $5-$10/corner (depending on how low the profile of the tire is). Goto www.tirerack.com
& see their recommended installers in your area, and how much they charge per-wheel/tire. $15/corner seems fair for an indie' shop, from which you didn't buy the tires from. Just reuse the valve-stems from your current tires (otherwise they run $2-$3 each).
Originally Posted by yeahplayer
Also..does changing rims void warranty in any way? (sorry I've never changed rims before)
No, the manufacturer's limited warranty will still be in effect.
Keep in mind that your '09 Accord LX sedan's wheels have TPMS (Tire Pressure Monitoring System) and the '98 Accord V6 sedan's wheels don't, so you'll have do something about the newly activated light on the instrument cluster.
Also, since your Accord's computer will sense TPMS-error, it'll therefore not allow you to deactivate your VSA (Vehicle Stability Assist, basically traction-control for when there is excess wheel-slippage detected). The VSA is generally deactivated for enthusiastic/spirited driving and/or when in snow/mud conditions where max' tire-spin/rotation is desired at low speeds to prevent getting stuck.