If I have a private key written down somewhere and for further security change one or more of the digits and then have the public address from the resulting private key written next to it.  How secure is that?  Would a brute force attack or any other attack be easier or no?  
Example private key  6108A178B39FF904C9F408741935554E042BDE257DB7F5621555175BACAC2A9C
Bitcoin Address        1GHVFk9HB2ke2UJsqTWWYiqVHemUyn8jTL