Dravidian languages like Kannada (and Telugu) have the nukta diacritic (಼) to represent foreign consonants, and Tamil has a special character (ஃ) which can similarly be used, as shown in the table below:
How are these consonants accurately represented in Malayalam script, especially in Islamic texts?
Why is there no nuqta like other Indic scripts? (especially given that more than quarter of Kerala's population is Muslim)
It looks like the parent script of Malayalam, Grantha script also has support for nukta at codepoint:
U+1133C. Why then is it not encoded in Malayalam script?