Rosemary tiles replacing

I have replaced some which I can get at from ladder a couple of rows up from gutter and had some replaced last year with builder and new ridge tiles.

I noticed a few more going house is 1920 semi. I know with age they get brittle and break when you replace some. But has anyone replaced any from inside in loft? I dont have any membrane in there roof is old.

From my understanding you need to replace tile above to slide tile below from the wood (cant remember name they call it) so the two prongs lift up. I know some old tile might slip down in to guttering.

edit I dont have any leaks and I know it might be hard tracing which tile need removing I got one bang in about 2 rows from top of ridge tiles.