SGS2 Replace preinstalled apps in Custom ROM Is is possible to change / modify the custom ROM you're about to install on your rooted Galaxy S2 (9100)?

Usually, I would install CyanogenMod 10 Nightly build. Then, I'd install GAPPS (google apps). Lastly, I'd restart and it would work.

Now, what I want to do is to replace a default CM (CyanogenMod) apps (SMS, Contact manager/Call manager) with those included in JB 4.1.2 (leaked version).

Is there any way to achieve it?

Thanks in advance for any info and suggestions.

UPDATED POST

Here is a pic of apps difference in icons (on left CM10, onright JB)
And here is a snapshot of apps in system/app/ of those versions
Since you're rooted within CM, its a matter of doing the following, provided you have read the following:
Caveat Emptor:
The Jellybean leaked apks are signed with the signature key used to generate the signed leaked ROM of JB, however, it may clash with CM's own signature key which is, and I'll guarantee, different, so may not work at all!
You are on your own from there onwards.
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remounting the /system rewriteable as in adb remount to make it writeable
replace the apk's concerned within /system/app by adb pushing the appropriate apks taken from JB, as in adb push name_of_jb_apk.apk /system/app (Repeat for each apk concerned) - this will overwrite the apk's already residing in /system/app
remount the /system as read-only as in adb remount

Reboot, and go into clockworkmod recovery and clear the data/cache, the reason being is to remove the old cached data that was in use by the old apk's, and thus, minimize the chances of force closes within the relevant apks in question.
I will list the actual filenames for the apk's concerned:

Sms, the filename is Mms.apk
Contacts, there's two apks involved, ContactsProvider.apk and Contacts.apk
Dialler, name is Phone.apk, now, beware, this may have a dependency on TelephonyProvider.apk also.

Whilst I have mentioned the actual apk's, I am therefore disclaiming any responsibility for anything that may happen on your handset as a result of replacing system apps.