The charity plans to build 12 lifeboat stations on inland waterways, and already operates from two stations in the Suffolk Broads and Northern Ireland, but requires formal approval from the Charity Commission.
This is needed to allow the charity to spend funds collected under its previous objects, on the new purposes.
If no public objections are raised to the scheme over the next month, the Commission will endorse the changes.
As a charity with a Royal Charter, the RNLI must also gain approval from the Privy Council, which is expected to be given this summer.
At the RNLI's annual meeting last month, the governors passed the necessary amendments to the charity's charter and bylaws.
Ian Ventham, RNLI's corporate services director, said that the expansion to inland waterways was a small change to the charity's work and would take place as part of a larger expansion of its lifeboat services, which has been going on for two years.
The charity is also rolling out a pilot lifeguard project, which started last summer, to more beaches in Devon, Cornwall and Dorset.
The project encompassed 27 beaches last year and will be expanded this summer to cover 47 beaches in another two local authority areas. The new project will cost ?xA3;1.5 million, but the RNLI hopes to recoup most of the money through donations from local authorities in the areas in which it is working. Fifteen full-time managers have been appointed to manage the 200 seasonal lifeguards working on the project.
"This is a major step for us. Lives are being lost and we think we can do the job more effectively than local authorities. It's about a joined up rescue service from beach to sea, co-ordinating the work we do,
The charity is also to begin work on a lifeboat training college near its headquarters in Poole, Dorset. Ventham said that whereas in the past, lifeboat crews came from a maritime background, this was rarely the case today and the charity had to invest in training new staff.
T he site, previously occupied by a chemical works, has to be first decontaminated but work is due to start in the autumn and be completed in 18 months.
RNLI also plans to set up two response teams to aid in future flooding emergencies in the UK.