Question about updating old post Date & SEO Ranking

hi,
I have one simple question..
As default WordPress showing latest post’s in front, but I want to show some Specific old post’s in front of the list, so i have to edit date of the old post to bring in front, So my question is is it bad for seo? because I am changing my post date ie. “31 dec 2014″ to 2 Feb 2015” just because i want to show it in front of list.
Is it’ll harm my ranking for that old post?

Is there any plugin to do this? (without changing date)

I hop you understand want i want to do : (show some old post in front of list. not wanna sticky post)

sorry for bad English. ??