A plpgsql question !

I am planning to enhance PgAccess in order to handle plpgsql functions
(to define, delete , inspect and modify them).

In this respect, I would like to know :

1. what is the value of prolang field in pg_proc table for plpgsql
functions (on my system is 43009, but it this value stable?)

2. are plpgsql functions interpreted at execution time ? If not (just
for the record) is this a big performance penalty ? Should I reconsider
writing them in "C" for triggers for example , or for the most often
called functions ?

3. in order to modify a function's source, to change to field procsrc in
pg_proc table ? Or should I "drop function ..." and "create function
..." again ?

Please CC: me directly to teo(at)flex(dot)ro

Thanks in advance,
Constantin Teodorescu
FLEX Consulting Braila, ROMANIA