You can. But, in this case it would be "sticks to" (with an 's').

No. They are two different words.

Thank you Ian! :-)

"insist on" often means to demand something of others (執意, 非要?), but it can *also* be used figuratively to mean someone always chooses something. whereas, stick to means to "keep with", "stay with", don't use other kinds.(kind of like 堅執, 堅持?）