(This is not SPSS-specific.) If you want your intercept to be a specific value (say, $17$), subtract that value from all $Y$ values and then fit your model while suppressing the intercept. Bear in mind that doing this is subject to all the same caveats as forcing your regression line to go through $0$ (cf., When is it ok to remove the intercept in lm()?, & When forcing intercept of 0 in linear regression is acceptable/advisable).

(This is not SPSS-specific.) If you want your intercept to be a specific value (say, $17$), subtract that value from all $Y$ values and then fit your model while suppressing the intercept. Bear in mind that doing this is subject to all the same caveats as forcing your regression line to go through $0$ (cf., When is it ok to remove the intercept in lm()?, & When forcing intercept of 0 in linear regression is acceptable/advisable).

(This is not SPSS-specific.) If you want your intercept to be a specific value (say, 17), subtract that value from all $Y$ values and then fit your model while suppressing the intercept.

(This is not SPSS-specific.) If you want your intercept to be a specific value (say, $17$), subtract that value from all $Y$ values and then fit your model while suppressing the intercept. Bear in mind that doing this is subject to all the same caveats as forcing your regression line to go through $0$ (cf., When is it ok to remove the intercept in lm()?, & When forcing intercept of 0 in linear regression is acceptable/advisable).