I think so. Try
<terms>
<locale xml:lang="en">
<term name="and">
<text>AND</text>
<symbol>$$$</symbol>
</term>
</locale>
</terms>
where AND and $$$ are your text and symbol and respectively. This might not be quite right, but you get the general idea - play around with it in the preview panel.
If I'm wrong and you can't define the symbol, you can still define the text and to be a symbol (that's definitely possible).

Has anyone come up with the idea of how to change "&" (ampersand) for another symbol? I still don't know how to do it :( I need a comma instead of &

I have one more problem. How to put a space after "p" i the page number in a citation. Instead of (Kuhn p.20) I'd like to have (Kuhn p. 20).

Thank you for your help and patience :)
Jacek

http://citationstyles.org/downloads/specification.html#name

The trick is to remove the "and" attribute from the cs:name element.

that depends on the style - the page number in citations is refered to as "locator" in csl.
The "p." can be addes either as a prefix
<text variable="locator" prefix="p."/>
I that case just add a space to the prefix:
<text variable="locator" prefix="p. "/>

Or it can (more likely) be added as a label variable, along these lines
<label variable="locator" form="short"/>
<text variable="locator"/>

In that case you'll need to get a space between the two:
You can do that using prefix=" " on the second line:
<text variable="locator" prefix=" "/>

THANK YOU adamsmith! :) I didn't know that page number is referred to as "locator". Now I can start writing my paper :)