can contsant tuning changing effect the string badly(i keep going from E to Eb and drop d)?

Depends on the guitar and playing and types of strings, but I would say constant retunings can make a string go out of tune more often yes. It can happen.

It can only affect strings but not the guitar (unless you retune the whole guitar every day up and down for a whole year). The neck is designed for a constant tension and once it gets used to it you should keep it that way. Changing the tuning of the 6th string only or a whole tuning just a half step down won't hurt but strings lose sustain quickly that way as you stretch them.

If the lowest you go is drop d and Eb the effects of changing tunings wont be quite so evident, but it will be there. Like Emir and Ivan said, it can cause strings to fall out of tune quicker and quicker and lose sustain over time. Best thing for it is to keep a constant tuning.

How constant changing?