@kuchaguangjie you can use the custom command feature @eht16 referred to for any kind of transformation like this, using any programming language you want. For example in Python you could make the up/down commands something like this (untested):
```bash # up python -c 'import sys; sys.stdout.write(sys.stdin.read().upper())' # down python -c 'import sys; sys.stdout.write(sys.stdin.read().lower())' ```
As for fast scrolling, a couple alternatives are to use the <kbd>Page Up</kbd> and <kbd>Page Down</kbd> keys (available on full US keyboards at least), and/or you could use the [Overview Plugin](https://github.com/codebrainz/overview-plugin/) to quickly jump over large ranges in the file.
If those aren't suitable and you know more Python than C, C++, or Vala, you could use [GeanyPy](https://plugins.geany.org/geanypy.html) to implement such a feature in your own plugin.