While I have never noticed changes in formatting of non-selected things when modifying a style, except for the formats of "bullets and numbering", I had problems with changes in adjacent apparently independent things by the insertion or deletion of formatted text.

To guard against such problems especially in paragraphs that use "bullets and numbering", where the font used for bullets and numbers appears to be linked with the font used on the associated line, I have become used to insert some random letter before the place where I would paste formatted text, if it is a place where this may not work as expected, which blocks any spreading of that format. After pasting the specially formatted text, I delete the previously inserted letter.

This undesired spreading of the formatting style happens only over white spaces and invisible control characters, it does not happen over normal printable characters, so inserting a printable character is guaranteed to contain the style.