Replace changing string including uppercase character with lowercase character

[silfer]

Thank you, again, scidam, for your contribution.
The problem remains for the ones who would be interested :
How replacing the first character of a word, marked by some preceding substring (in my case : <lb/>), by the same character but lowercase.
I repeat my example :
Input :

<p>Material blabla ; <lb/>Dimension blabla ;<lb/></p>
<p>Sideral blublu ; <lb/>Sticky Gonzalez blibli; <lb/>Reductio ad absurdum bloblo</p>

Wished output :

<p>Material blabla ; dimension blabla ;<lb/></p>
<p>Sideral blublu ; sticky Gonzalez blibli; reductio ad absurdum bloblo</p>

If no one from you, distinguished programmers, has any idea, should I conclude that no solution is available?
Take care, everyone.

[silfer]

Hello.
This is a strategical post to place my thread at the list top
Cordial greetings.