How to add custom music to RCT1/2/Locomotion

This tutorial assumes you already downloaded Audacity. Get it at http://audacity.sourceforge.net/download/
You'll also need the FFMPEG library. Instructions on how to do this at http://manual.audacityteam.org/o/man/faq_installation_and_plug_ins.html#ffdown

1) Open the audio file you want to convert.
2) Select Track > Resample... and enter "22050" into the box.
3) Select File > Export... and select "Custom FFMPEG Export" in the Save as type dropdown box.
4) At the bottom left of the Audacity window, change the Project Rate to 22050.
5) If the song is too loud (the dark blue part is touching the top and/or bottom, circled in red here https://i.imgur.com/BlNxTQe.png), select Effect > Compressor, then click ok in the dialog box. Afterwards, the track should look similar to the bottom image.
6) Click Options, select "WAV" in the first box and "pcm_s16le" for RCT2/Locomotion or "pcm_u8" for RCT1 in the second box. Enter 22050 into the box marked "Sample Rate". Leave "Tag" blank and "Bit Rate" 32000. Click OK.
7) Save the file as CUSTOM1.wav or CUSTOM2.wav, or as cssXX.dat, where XX is the number of the in-game track you wish to replace if you're doing so.
8) Drag the new audio file into the Data directory in RCT's install directory. Backup the old audio file if you're replacing an existing in-game track.


Notes:
If the filesize of the song you are replacing the existing music is larger than the filesize of the game's song, the game will cut off the song at the filesize limit (tl;dr the whole song won't play). If this happens, try replacing a song that is larger than your song.
If you want custom music in Locomotion, your only option is to replace an existing track, as it doesn't support custom music by default.