If I understand correctly the problem, it all boils down to changing the global appearance of the document in a few steps.
If your document is fully styled, i.e. you never used direct-formatting all over your document and exclusively worked with styles, the text parts can be changed very easily for larger font size. This requires managing very rigorously your styles.
Remember that all styles are organized hierarchically, with Default Paragraph Style being the common ancestors to all. However, some built-in styles creates "breaks" in the inheritance:
- Heading, ancestor of all heading and titling styles
- Index, ancestor of all TOC, bibliography and index styles
- List, ancestor of List n and Numbering n styles and derived ones, usually used in lists
- Caption, ancestor of targeted caption styles
These may be configured for font face and size in Tools>Options, LibreOffice Writer>Basic Fonts (Western) and this is where you create the "break" in inheritance unless you don't use the feature and configure the styles in their definition using the following rule.
To minimize the number of fixes when you decide for a new base font size, make sure that where you change font size (if you don't touch at all the parameter, it inherits from the ancestor; but whenever you click on a size, be it the same as the ancestor, you freeze the parameter to this value) the new size is defined in % units so that it is recomputed whenever it changes in the ancestor.
E.g., if size in Default Paragraph Style is 12pt and Heading is 14pt, respecify Heading size as 116% or round it to 120% which is more user-friendly (not for the end reader but for the editor).
The same can be done for vertical spacing but nit is a bit more tricky because it requires to list all used styles to compute sensible values.
Don't code font size changes in character styles. Character styles are also organized, if needed, in a hierarchical way, but only between themselves. %-units are relative to their user-created ancestor, not to the paragraph in which there are applied. A character style should only change "non metric" parameters like weight, angle, ... Unfortunately, subscript and superscripts are "metric" changes. They should receive their own styles so that only these need to be adapted in case of a global font size change.
Tables should not be a problem as long as you have used so-called table styles to format them because these in fact collection of macros direct-format the table and the cells and take over whatever you do to them.
Standard manual tables extend from margin to margin. The width therefore cannot be extend. If you manually set the width smaller than the distance between margins, of course it will not change either.
Text inside the cells is styled, which means it ultimately inherit from Default Paragraph Style. If your initial document requires that table text be set in different size than the text, modify Table ... (more)
