Can I find and replace something in a variable?

Can I find and replace something in a variable?
JW Player requires the & inside a file name to be url encoded.
However when I urlencode a tinybutstrong variable of a file name using the "htmlconv;url" parameter, the & does not change to %3F
Can this be achieved?

Hi Desbest,

"htmlconv=url" does replace '&' with '%26'.
'%3F' is for '?'

In fact "htmlconv=url" calls the PHP function url_encode().