You needn't change that. LibO Calc will do it for you.
-1- Select the range containing the numeric results or contents you want to copy and to paste to a different application.
-2- > 'Format' > 'Cells' > tab 'Numbers'
-3- There you can use a dropdown list under 'Language' to select a language. Choose 'English (UK)' e.g.
The language (in fact a "locale") is associated with rules concerning the display of numeric values. For English locales this will include the usage of the point as the decimal separator.
(Sorry. Posts crossed. A named cell style is clearly preferrable over direct formatting.)
By the way: Can't you set the CAD program to accept decimal numbers with the comma as the decimal separator?