Please see the following advice from ESS (SIMS Software developer) & DFE.
Gender should be self-declared and recorded according to the wishes of the parent and/or pupil.
Individuals are free to change the way their gender is recorded. There is no requirement from the department of education for any legal change or gender recognition certificate and it remains open for the school to amend the gender of any pupil, within their own MIS, at any time.
Male and Female are currently the only options for gender in SIMS, and it is not possible to create new genders. In the School Census, there are only two genders which are statutory Male & Female. We recommend discussing this issue with the DfE for clarification. If a school wanted a field to indicate locally of a different gender they can always create a User-defined field. Please follow https://faq.scomis.org/kb9359/ on how to do so or you could add a Quick Note in the student’s record that details the date of this change so that it can be recorded in SIMS.
There is currently a change request logged with ESS to add different options into the gender area, these are currently under consultation with ESS and might be included in a future upgrade of SIMS.
While Male and Female are currently the only options for gender in SIMS you can add and neutral titles such as Mx in place of Mr/Mrs/Ms by going to Tools > Looks ups > Maintain > Search Title in the description field > Click New > Save.