If you are making changes to theme files, you should be using a Child Theme –
http://codex.ww.wp.xz.cn/Child_Themes
If you mean customizing via theme options/settings, those won’t get overwritten. Still always make a backup before updating.
Does that mean, after applying http://codex.ww.wp.xz.cn/Child_Themes
if I update the parent theme, its customizations will not be lost..??
Correct – though you will have to move any changes you’ve made to theme files to a child theme.
Yeah I read the details here.. http://codex.ww.wp.xz.cn/Child_Themes
but I don’t remember the specific changes I made.
So, its kind of a risky job as if an error is made, it may break whole thing.
Everyone would prefer if there might be some automated option. Thanks though.