Welcome to the site !!
Actually , you could have started your own topic about this , as this is a 10 year old post ...... but with that said ......
Yes , the spring will fit , the spring size is for your weight and/or speed/skill , not for the bike weight .... for the most part ........ The stock spring rate for a 250R for the Fork is 0.45 or 0.46 (depending on year) , and for the Shock is 5.3 ..... The 250X standard spring for the Fork is 0.42 and for the Shock is 4.80 , they run a softer spring to keep the suspension plusher in the initial part of the stroke but the 250 is sprung for someone no more than about 150 lbs max , but if you are re-springing for your weight , then go with what spring is required for your weight , so if you weigh 180 for example , you would want a 0.46 or 0.47/5.5 . but the springs will fit , both fork and shock for 250 and 450's you can swap springs around , if you are in the target weight of the 250 stock springs are fine , if not then look for a 450 spring , or aftermarket ...
Since you did not give your weight , I can only speculate as to what spring you actually need , .... Personally , I spring heavier on the X because the bike itself weighs more , so when compressing the suspension , it actually compresses farther on the same obstacle than the R , and usually when riding a X you have a backpack full of stuff that makes your (guessing) 150 actual weight , seems like 165 to the bike , because you have 15 lbs of extra stuff on , as opposed to riding MX ..... Again , if you are just simple trail riding and nothing more , then you don't need a real stiff spring to compensate for the extra weight of the backpack etc. , just heavy enough for your weight ........
For a example , I run a 0.52 fork and a 5.5 shock on my 450X .... But.... I revalved it basically like a Endurocross setup , so it is sprung heavy to keep the forks up in the stroke , but valved very soft with fast Rebound , to hit obstacles hard (watch a Endurocross race and watch the suspension work , that is how I setup my X .... My 450R , I have it valved soft in the initial part of the stroke , and somewhat firm in the middle and end of the stroke , I have it sprung 0.47/5.8 , I am around 200 lbs .... Valving does play a part in spring rate choice , as does the type of riding you do and your skill level , faster rider , stiffer springs , heavier rider , stiffer springs ....... with stock valving , spring for your weight unless you are really abusing the suspension like would be in Endurocross .... For simple trail/off-road riding , you do not need real stiff springs as they will beat you to death .... unless you are really fast....
The softer the springs , the softer the ride ... to a point , if you are compressing the suspension more than 1/4 the way while just sitting on the bike , you are too far in the stroke and need stiffer springs to bring the forks (and shock) back up in the stroke , the mid stroke is usually harsher , so if you are starting there , the bike will feel harsh when hitting stuff and deflect all over the place in ruts and in rocks , clickers won't help much ....the correct rate spring will eliminate most of that , and you can be at close to stock clicker settings ....