Don't think any fork or lift truck manufactuer would approve of this modification and if they don't then the regulation probably says something to teh affect "it ain't approved, by the manufactuer,in writing, don't do it".
But with this type of modifcation, when an accident happens help keep our "ambulance chasing" lawyers & expert witnesses - happy, happy, happy & gamefully employed in the USA.

You might want to check what your own country & the manufactuer of the lift truck brand(s) says about this - 'casue what we do here or in other countries - may or may not apply to your situation.