Change Appearance has no effect on a Sim's DNA.  If you want the custom hair to be passed down in the DNA, then you have to alter the SDNA information in SimPE.  Do the following:

1) Open SimPE, use Sim Browser to find the Sim you want to modify, then click OK to bring up the Sim Information screen.

2) Click on More, then Open Sim DNA.  This will display a screen with genetic information (hair, eyes, skintone).  The top half is dominant, the bottom half is recessive.  Replace the string for the hairstyle in the top half of the screen with the string that corresponds to your custom hair.

For example, replace the Maxis default brown hair
00000002-0000-0000-0000-000000000000
with
acf276bb-4c70-f9a0-386e-cf96a987570f (or whatever the code is for your particular custom hair)

3) Commit.

4) Save your neighborhood file and exit SimPE.

If you do not know what the code is for your Sim's current custom hair (the one you're trying to make genetic), you can find out by doing the following:

1) Open SimPE, go to Sim Browser, find the Sim, click OK to view their information.  Click on More, then click on Open Character File.  This will close your neighborhood file, so be sure to save when prompted to do so.

2) In the character file, click on Age Data.  Now look at the plugin view, find the string labeled "haircolor" and click on it.  This is the code for the custom hair the Sim is currently using.

I have used the above methods many, many times in the last few months.  All of my Sims (except townies) have inherited custom hair.  I find it makes for a lot more variety, especially with toddlers.

Karen