According to the workshop manual
Section G6 - Hydraulic Accumulators. mentions "2. Clamp the sphere in a vice fitted with jaw protectors and using the special tool RH 8144 remove the clamping". But this tool (even if it is documented) can not be found currently.
Source: Workshop manual

British tools substitute
A pro in the US, Kelly Opfar, sells a sbustitute of the RR original tool, it can be seen working here http://au.rrforums.net/forum/messages/17001/34377.html?1546892840 It is expensive but you don't have to build it yourself.
Source: The Rolls-Royce Forum - Australia

Another method
Developed by Mr Leonard Stampton http://au.rrforums.net/forum/messages/17001/32756.html?1545341684
Source: The Rolls-Royce Forum - Australia

Here a tool by Mr Brian vogel
http://au.rrforums.net/forum/messages/17001/17918.html?1457735791
Also documented here (more pictures and explanations) http://au.rrforums.net/forum/messages/17001/12247.html#POST21382
Source: The Rolls-Royce Forum - Australia