Hi blackdog
What you mean by getting full access to external SD card? Are you planning to move applications from internal storage? As I know external SD supposed to be used to store pics, videos and docs. Everything else should be kept on internal storage but sometimes (especially in low budget devices) internal space is poor and then some apps can be moved to external SD.
if you want to just view, copy, paste, move all your saved files on SD card you just need to just install some File Manager like ES File Explorer which allowed you to do some operations without rooting and much more when you root.
Most of the smartphones can be rooted without any worries, just post what is your model.