i have Samsung gt-19082 i recently rooted my phone and added cosmic cm 11, but i have a smaller SD card ? i want to know is it safe to change the SD card ? (as during installation we add all the ROM , g apps on the SD card . i am a newbie at this
During flashing of ROM your ROM is installed to your device from files kept in your sdcard to your internal storage, mainly /system and /boot partition. So it should be safe to replace your sdcard.
For TL;DR It is definitely safe to replace your external SD card for a new one.
A normally working system will continue working normally. However there is no guarantee that all your apps will work correctly, as some of them may store extra info on your external SD card, like image caches (this is different from normal caches, some caches regenerate but others don't, e.g. image cache from the most popular instant messaging app in China, WeChat) and Link2SD. Most apps are designed to store only 'unessential' data on external SD card, so there's just a small matter of some network traffic to reload those caches.