1A fuse instead of 1/2A fuse: any problem?

Do so @ your own peril. Not a good idea to up fuse raings in electronics.

really bad idea. Have you checked out HiFi Tuning fuses? they have fuses at the rating you need (500ma). MusicDirect.com carries the HiFi Tuning line if you are interested, check em out.

If you need to deviate you want something that will blow sooner rather than later. A 1A fuse won't blow as soon as a 0.5 amp fuse. It will tolerate a higher "spike" that might damage your equipment. Replace fuses as recommended by the OEM or with a lower amp rated fuse if you must deviate.