In case there are no official Christmas track, I found a trick: you can put special music within Christmas (or xmas for an older version) > season > "folder for Org or Ogg".
Example: Let's use Org for this example. Download the Christmas Orgs from Fan Works > Music, under Org/PxTone > Wedge of Cheese, click Christmas Orgs (Batch Download) to download the zip file. (Name is misspelled, it is Cheese, not Cheeze, Andwhyisit, don't confuse Wedge of Cheese with GIRakaCHEEZER. That misspelled name was there all these years!)
Place all Orgs from the zip file to the newly created 'Org' folder, place 'Org' folder within Christmas > season and copy all the drum wave files from base > Org to Christmas > season > Org. Open the context file and find which songs are for. Rename the Christmas named Orgs with short names of the official name, for example (Mischevous Robot is 'wanpaku', Plant is 'plant', Oppression is 'ironh', Cave Story is 'curly', Quiet is 'quiet', Scorching Back is 'wanpak2', Geothermal is 'grand', and so on...).
Once you renamed all of the Orgs to match the names with the ones in base > Org, you now have the Org folder ready within Christmas > season. Launch CS+ from Christmas Eve to Epiphany, set music option to Original and the program ... actually plays the ones from Christmas > season > org !
Hint: If you want to change Wind Fortress music, use child (old) for Wind Fortress, rename child (old) to kaze within xmas > season > org.
For Curly Story, while there will be seasonal art, you will have to modify MyChar.bmp, NpcCurly.bmp & NpcRegu.bmp (don't try Caret.bmp, there is no such drown sprite for Santa Costume Curly) to play as Santa Costume Curly by finding the sources and editing them very carefully (you also need to increase color depth to 24-bit if possible).
If you don't want to modify them and want my modified Curly spritesheets for Curly Story, you must PM me for those, then swap the original ones with Christmas ones while Seasonal Art is available, leaving the originals stored. (This will also apply for Halloween art)