Yes, you may freely change and wash your الإحرام garments — the state of الإحرام is maintained by your intention, not the specific pieces of cloth.
Yes, changing الإحرام garments is fully permitted and does not affect your state of الإحرام in any way. The state of الإحرام is a spiritual commitment entered through intention (niyyah), not a property of the physical garments. You may change to a fresh set of الإحرام cloths whenever you wish — whether because the current ones are dirty, wet from sweat, or simply for comfort. Many الحجاج bring 2-3 sets of الإحرام garments for this purpose.
You may also wash your الإحرام garments during the الحج. Use unscented soap or detergent to avoid violating the perfume prohibition. Washing and drying الإحرام cloths is perfectly جائز. Some الحجاج 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 الإحرام 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 الإحرام garments at all times is مستحب, especially during the days at منى and عرفة.
Source: ابن عثيمين, Majmu Fatawa, section on الإحرام