How to preserve custom locales across glibc-* updates?

Issue

• How to preserve custom locales across glibc-* updates?
• Why does customized locale info disappear after updating glibc-*?
• How to preserve custom locales after glibc-common re-install?

• After updating glibc and dependent packages, some locale info is missing from the output of # locale -a.

  # localedef -f WINDOWS-31J -i ja_JP ja_JP.SJIS
  
  # locale -a | grep ja
  ja_JP
  ja_JP.eucjp
  ja_JP.sjis   <===  here it is.
  ja_JP.ujis
  ja_JP.utf8
  japanese
  japanese.euc
  
  # yum update glibc -y
  (..SNIP..)
  
  # locale -a | grep ja
  ja_JP
  ja_JP.eucjp
  ja_JP.ujis
  ja_JP.utf8
  japanese
  japanese.euc
  
   /*  ja_JP.sjis is missing  */
  

  Why does this happen? And should I define it again?