The move gives the board power to call a ballot of members to fill board positions as they arise. It was previously very difficult for the wider membership to nominate people to the board, or be nominated themselves.
IRS director-general Andrew Hawkins confirmed the IRS would put the new open system into action this year, holding an autumn ballot of its members.
There are four board vacancies to be filled this year. The change was agreed following the society's AGM last month.
Other constitutional changes include a limit on the maximum term for board members to encourage more members to get involved in the management of the group.
Board members can now serve no longer than five years on the board before standing down for a year, as opposed to the previous eight-year cap.
Those in officer positions, such as chairman, deputy chairman and treasurer, can serve for a maximum of three years.
Hawkins said the changes reflect the IRS's aim to be more 'transparent and democratic': 'The changes are designed to make sure we stay close to our members - we want to send the message out that this is not an old mates club, this is the member's professional society and they own and run it.'
The IRS also scrapped the positions of secretary and vice-chairman at the AGM, alongside re-electing College Hill consultant Richard Bowler as chairman and independent IR consultant Alexandra Hockenhull as his deputy.