Yes, you may freely change and wash your Ihram garments — the state of Ihram is maintained by your intention, not the specific pieces of cloth.
Yes, changing Ihram garments is fully permitted and does not affect your state of Ihram in any way. The state of Ihram is a spiritual commitment entered through intention (niyyah), not a property of the physical garments. You may change to a fresh set of Ihram cloths whenever you wish — whether because the current ones are dirty, wet from sweat, or simply for comfort. Many hacilar bring 2-3 sets of Ihram garments for this purpose.
You may also wash your Ihram garments during the hac ibadeti. Use unscented soap or detergent to avoid violating the perfume prohibition. Washing and drying Ihram cloths is perfectly permissible. Some hacilar wash their garments in hotel rooms and hang them to dry overnight.
The only requirements when changing are that the new garments must meet the same Ihram specifications: for men, they must be two unsewn, unstitched white cloths without any perfume or fragrance. When changing, be mindful of the head-covering prohibition for men — do not accidentally pull cloth over your head while removing or putting on the rida (upper garment). The process of changing should be done modestly, preferably in a private area. Carrying a spare set of Ihram garments at all times is sunnet, especially during the days at Mina and Arafat.
Source: Ibn Uthaymeen, Majmu Fatawa, section on Ihram