Yes, although sometimes d- does not mutate when it follows a word ending in -s. Nos da is correct, for example, and * nos dda is considered wrong, similarly wythnos diwethaf (last week) is usual, despite nos and wythos being feminine.
Apart from those two and one or two other long-established set phrases, it seems to be usual to mutate the d- these days.
So, 'Dw i'n actores da' would mean 'I am a good actress'. :p Best line i've learned so far.
Not quite good enough to get you a part in a Welsh play...
- Actores dda dw i should get you there, though.
As explained in the Hints and Tips, when discussing names, roles, jobs and so on, the name, etc, comes first in the sentence,