OK, this is specific:
I have a content type with two fields:
WHAT I NEED:
When there is 15 days left for the expiration date of a specific node, the select list field from that node should automatically change to "yellow".
Is this possible using, for example, rules module? Is there any other option?
Hmm.. This sounds like it could be done with Rules and VBO.
date field > relative date. You might also want to filter out nodes that have already been changed.
Create a rule:
Set a data valueif it's a single value field or
Add item to listif it's a multi-value field.
EDIT: As of November 2017, this feature whereby VBO supplies Rules has been a bit broken and requires a patch to work.