Yes it is possible, DataDynamic have some special commands useful to hide categories while keeping the base and all the calculations fixed on the original number of cases.

There are 2 ways you can achieve this, depending on the complexity of the table (amount of variables and categories involved). 

+ Most of the times, when designing the table, click on the 'filter icon' next to the variable name. Un-check the categories you don't like to see in your table (in this case 35-49) and run the table. 

The obtained table will look like this (without category 35-49 but with all the rest calculated as if the category is there)

+ in some more complicated cases, the number of categories is really big and you're trying to find a way to quickly combine categories that you want/not want to see.

If the above table is the original one, select with your mouse the categories you want to keep (i.e. Uk, France, Germany, Netherlands): they become yellow once selected. 

Right-mouse click on the selection and select 'combine add' and choose the group to appear 'at the bottom'. In this example the group is named 'UFGN'.

This way a group with the selected categories will be created at the bottom of the table, just above the 'Totals' row. 

To now show only the new group created, click on 'Table options'->'Formatting options' tab and on the right corner select (in this specific example) 'Hide categories rows'. This way all the categories will not be displayed but the one that we've just created. It is there because since it has been created 'at the bottom', DataDynamic recognizes it as an extra row and so is the only one not hided.