CPC is not a parameter that you can set. What you can set is your bid, thus making sure that, in any event, you won't be paying more than that, for a click (if you do not have bid modifiers in place or if you're using enhanced CPC).
But as you can see here https://support.google.com/adwords/answer/6297?hl=en&ref_topic=24937 , CPCs are related to your Ad Rank, which in turn is related to your Quality Score.
What you can do, without touching the current keyword set (since you say you don't want your campaign to be affected) is to make sure you write the most relevant ads possible and make use of all available extensions, in order to raise you CTR as high as possible.
Another thing you can do is work on your landing pages and make sure they are as relevant as possible with respect to your keywords.
If you manage to raise your CTR, your QS will increase and if the QS increases you'll end up lowering your CPC.
Some more tips can be found here https://support.google.com/adwords/answer/6238826 and here https://support.google.com/adwords/answer/6167123?hl=en
Hope it helps.
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