Good news for Inception users. How to install & use HSDK only with Inception (without Harmattan open mode) :

1) Installation :
- install Inception and Easy Chroot following the Easy Chroot instructions for Inception user;
- download & install HSDK 0.0.1 from post #7, just by tapping it with a file manager or via "# dpkg -i hsdk_0.0.1_armel.deb" as root;
- download the Harmattan SDK rootstrap as explained in 1st post;

2) Creating the SDK.img in MyDocs (only 1st time) :
Once after reboot it is needed to give chroot permissions, so go to the X-Terminal as user :
$ ariadne sh
type the root password, then :
# /usr/sbin/aegisctl -s
which gives extended permissions to mount images, check them typing "accli -I" to show more than 200 lines of credentials instead of just 6 default credentials.
Finally :
$ hsdk -i
just confirm the questions. It takes some minutes reading the "arm-public-sdk-rootstrap.tgz" compressed rootstrap and creating the SDK.img (image of Harmattan SDK) with 2.86 GB (3,000,000,000 bytes) and 441 MB free.

3) Everyday use of HSDK :
Do not use the HSDK icon, it doesn't have the extended permissions to mount the image.
Once after reboot it is needed to give chroot permissions, so go the X-Terminal as user :
$ ariadne sh
type the root password, then :
# /usr/sbin/aegisctl -s
which gives extended permissions to mount the image, check them typing "accli -I" to show more than 200 lines of credentials instead of just 6 default credentials.
Finally :
# hsdk -s
starts the Harmattan SDK on your device. After finishing your compiling and packaging :
# hsdk -e
closes the Harmattan SDK image.

PS : I confirm that installing hsdk_0.0.3_armel.deb on Incepted Nokia N9/N950 (without Harmattan open mode kernel) yields a reboot loop & need to reflash the device. So, for Inception users : do not use hsdk_0.0.3, only hsdk_0.0.1.