Facebook ad creatives are broken down into 3 parts and their importance is weighted as follows:
Image - 70%
Headline - 20%
AdCopy - 10%
If the adcopy is only 1/10th of a factor in affecting the CTR, guess how much it affects CR%?
short answer: 0%
long answer: zeroooooooooooooooooooooooooo percent
If you want to tweak your CR%, rotate offers to see which one converts best, this is if you're direct linking. If you have a lander, then you should be split testing variables on your page. Adcopy has little to nothing to do with CR% on FB.
For FB, you should always try to optimize for a good CTR, but if your offer doesn't convert then you're pretty screwed too, so test both simultaneously.