I understand that the area within my flat falls under my private jurisdiction in terms of changing the interior design, etc (as long as they're within the HDB guidelines), amongst others. And I am also aware that whatever lies beyond the main gate/door of my flat shall not be altered in any way as they belong to HDB.

As such, I would like to know if there should be any penalty whatsoever that may arise if I changed the HDB-issued bell switch outside my door to a bell switch of my preferred design.

Refer to the photos below:

Original HDB-issued bell switch

My new bell switch

Edited September 15, 201412 yr by Remy Yosef

I doubt this will bring much problem to you even if it is not allowed by HDB.

I believe they should be more concerned about unauthorised usage of HDB's space than such switches.