named expression type- change

Hello all,

I had come across a situation where I had created a named expression with type length(mm unit), which was supposed to be constant type.

Created dimenion then used in several sketches and several times.

Finally I realised the mistake and wanted to change. When I get in to expression list it didnot allow me to change the expression type untill I changed all references to other expression.

is this how it intent to work ? or am I missing something here?

help me on this !!!!!!!!!!!!

thanks in advance..

NX10.0