Need to pass a 200K+ HTML literal string to a CLOB in procedure

Due to application requirement, I need to create a script, which will reused to load dynamic HTML format 200K string to a stored procedure in CLOB.

When I use the string as is, it fails with 'buffer too small' error. Then I tried using SUBSTR to divide in smaller strings of 32K size each then appending one by one but doing this loses HTML format and puts everything in single line which is again failing to load giving 'string literal too long'.

Is there a way to use SUBSTR or any other function to retain the formatting?