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

Actually you have QUADRUPLED the power that can pass since power is proportional to the square of the current.

Fuses DON'T blow at their rating. The rating is the current they will carry forever (almost). As current increases over the rating, the time until the fuse blows decreases. A half amp fuse will, depending on type, blow quite quickly at one amp, whereas the one amp fuse will not blow.

Put a 2a or a piece of wire in there, then you won't have to worry about those wimpy shutdowns.

Oh, and I should have added - keep a fire extingusher handy

You can order those size fuses from most all the big electronic parts stores or maybe even you local electronic parts store or even Radio Shack. If it was a slow blow .5A you can use a 1A fast blow, but it is better to stay within the design. I have tried the HiFi Tuning Line fuses (very expensive for a fuse) and did not notice any change in sound. Might have been one but it is too small to tell for me.