import re
text = '"Link To Wikipedia":[http://w...content-available-to-author-only...a.org/]'
print re.sub(r'"([^"]+)":\[([^\]]+)\]', r'[[\2][\1]]', text)
aW1wb3J0IHJlCnRleHQgPSAnIkxpbmsgVG8gV2lraXBlZGlhIjpbaHR0cDovL3cuLi5jb250ZW50LWF2YWlsYWJsZS10by1hdXRob3Itb25seS4uLmEub3JnL10nCnByaW50IHJlLnN1YihyJyIoW14iXSspIjpcWyhbXlxdXSspXF0nLCByJ1tbXDJdW1wxXV0nLCB0ZXh0KQ==