LibreOffice doesn’t support “conditional styles” as a specific kind of styles. (Don’t know what Excel does.) Cell styles used for overlaying attributes under conditions in CF are defined the same way as any cell style. This includes the full working of heritage.
Thus: If the cell styles for conditional application are derived from a common base cell style, you only need to modify this single style to get the change to work for all the styles inheriting from it and not having the respective attribute explicitly set to a different value.
When converting an Excel document to the native format of OpenDocument applications, always the set of automatically created styles shoud be inspected and reworked to get consistency concerning the clear and effective style concept available here.
After reading superficially through the mentioned bug tdf#34412 I wouldn’t expect a definite solution there. The sheet/document models may be too different insofar.