kati sutram - significance and practices

[Raghav K]

My pranamams to the members of this group!

There is a practice of changing yajnopaveetham around the shravana purnima/upAkarma time apart from other incidental occasions. Wondering if there is a similar recommendation for changing the kati sutram (waist thread) and if there are any pramanams in the scripture for this. 

Related to this, I have a few more questions.

1) Are kati sutram (waist thread) and kamara bandha (waist belt) the same? Or are they different? Were they both worn or was only one of them worn in ancient times?

2) Was their purpose only functional (like to hold a kati vastram/kaupeena or a pancha kaccham/veshti/dhoti) or as some would say this was to prevent hernia when lifting weights or, is there a scriptural, more AdhyAtmika reason behind wearing this? ( I heard from someone on one occasion it was to prevent asuric forces from spreading from below to above waist but never understood what that meant or if there was a pramanam to this in the scripture. I had no direct contact with this person.) 

3) If it is recommended in the scripture, was it only recommended for dvijas, or all men or was it for both the genders?

4) Do they still hold relevance in the modern context where most people have moved away from wearing a kaupina to undergarments that already come with  elastic bands and pants that are mostly supported by belts? I mean do they still have to be worn because the dharma shastras recommend them (if they do)?

Thank you for your patience and guidance,

Warm regards,

Raghav