Modifying a .chart's BPM without moving the notes
You may have charted a song at 90 BPM when it really had to be 180 BPM. No worries, mistakes happen! Here's a script that can (hopefully) fix that.
Default multiplier is 2 to double the BPM. You can use 0.5 to half the BPM. You should also definitely check if everything looks right afterwards, notably sustain lengths.