Can we modify 'text *' passed to a C function?

If I write a function that does a 'tolower()' on each
character of a parameter passed into my function, do I
have to allocate a new text object and initialize it
and copy the data, or can I modify that object in
place and return it?

Modifying it in place will save the overhead of an
alloc call, and on a large database, that could add
up.

right now, I am allocating a new data buffer of
exactly the same size and it seems like a waste.

Secondly, if I modify the data length of an object,
as: VARDATA(field) = nn, making sure that 'nn' is
smaller than the origial length, with this affect the
memory management?

In short, can we modify text * objects passed to a C
function, and can we shrink the length field without
any ill effects?

(Doing so will reduce quite a bit of memory allocation
overhead I am doing.)

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