Does google bots index page again if updated

I have one general doubt to be clarified and i hope u guys will tell me more abt this. If i change title, header of posts once its been indexed by the google. I have a blog. I have been changing the title and header of several posts once they have been index by google. I have been doing that regularly. Fact is that i also see the changes on posts in serp of google. Will it hurt my blog? in serps? in pagerank? any way or

will it benefit my blog bcz am changing it according to required keywords? Actually i add more lines to previous work like if title is like :

hi, i am xyz
-> hi, i am xyz and how are you?

 

it will help if you do it right with the proper keywords.

 

but i have heard that its harmful to change anything in post once u publish it and it has been indexed by google?

 

Yes google bot will index the pages after you will update them

 

Don't write posts according to the keywords..
and Yes. Google will update and index the page again.. but it may take sometime.

 

google will crawl your blog regularly if you keep chaning the content. This is imporved further if you upload a sitemap which lists the structure of your site

 

so u mean that its no problem if i change sometimes content and make changes in the post (i have blog). Hope it isnt harmful.

 

Yes Google again indexed your updated contain again.