The rules are here
https://www.easa.europa.eu/sites/def...s-08042012.pdf
If you are flying EASA aircraft it is not just differences training in the general aspect of the aircraft such as tailwheel/CS prop/pressurisation but in individual variants though this can just be a briefing and or reading the flight manual FCL.710 addresses class and type ratings concerning variants.
In order to extend his/her privileges to another variant of aircraft within one class or type rating, the pilot shall undertake differences or familiarisation training. In the case of variants within a type rating, the differences or familiarisation training shall include the relevant elements defined in the operational suitability data established in accordance with Part-21.
Differences training requires the acquisition of additional knowledge and training on an appropriate training device or the aircraft. Familiarisation training requires the acquisition of additional knowledge (GM1 FCL.710)
If you are flying any of the following you need specific difference training on the variation that needs an endorsement and these are all additions to the straight SEP (Land) - you may note that there is no SEP(LAND) with nose wheel, though if you have done all your flying on tailwheel it would be daft to jump into one without at least a checkout and I doubt that anyone would hire you an aircraft without anyway!
SEP (land)
SEP (land) with variable pitch propellers
SEP (land) with retractable undercarriage
SEP (land) with turbo or super charged engines
SEP (land) with cabin pressurisation
SEP (land) with tail wheels
SEP (land) with EFIS
SEP (land) with SLPC