I have heard that there are traditions that say if you want your child to be beautiful, or righteous, or some other merit, then you should do this or that thing. Then you should do this or that thing

Or one should perform the intercourse with one's partner on certain days.

by

Yes we do have such traditions. One’s state during conception does have an effect on the child.

You may see this book about some of that etiquette:

https://www.al-islam.org/marriage-parenthood-heavenly-path/chapter-2-sexual-etiquette