You can is the amp is can only be supplied if the load is actually pulling that much current. Ohms Law always applies.
I am assuming that the load in this case remains the same then you can use the transformer you mentioned as long as power rating remains the same. However if the transformer is part of a load which keeps changing such as a power supply then replacement of the transformer will mean the circuit will draw more current.
downstream wise 1A is 2x of 0.5A so you are okay. larger capacity.
but you may wish to check if the upstream is rated for up to 1A current. Otherwise your transformer, if pulling a 1A load, may trip up (over amp?) the upstream power devices. Just saying.
My advice is not professional and I have stopped practicing engineering for a long long time. besides, I'm just a cat. meow
Since Sion mentioned it's for external harddisc, I presume it's more like a DC power supply rather than an AC transformer.
Under normal condition, a higher capacity power supply should work fine.
But sometimes, electronic manufacturers use dedicated power supply to limit the current for abnormal conditions.
Abnormal conditions like a shorted internal electronic component or a stuck motor would draw too much current which could result in overheating.
So it would be best to use the correct power supply