list if strpos(var,"x")>0

replace var=substr(var,1,length(var)-1)+"000" if regexm(var,"X$")
*or
replace var=reverse(var)
replace var=subinstr(var,"X","000",1)
replace var=reverse(var)

stata提示
option if not allowed

stata提示
unrecognized command:  reverse

destring var,gen(newvar) force
gen newvar2=newvar==.
(preserve)
keep if newvar2==1
(restore)

已改正，这些问题如果提供数据就容易多了

如果你的数据只有末位是x的可能的话：replace var=subinstr(var,"x","000",.)

var
1604666
00160704X
1607138
00162195X
00162208X
1622282
1668029
00176423X
1771667
1834488
00930430X
FN1313052
FN1313060
FN1315357
FN1316181
A06439180
A19439761
A19439825
A19440834
X18061661
X18061741
HB9993153
HB9993196
HB9993313
HL001367X
HL0113814
HL0187135
A06439017
A06439180
GS8511938
GS8513554
GX2588078
GX2810249
GX2810265
A80611778
A80611989
A80616843
A80617256
AH6404107
AH6404190
AH6404203
B0759098X
B07591069
BC0400147
BC0700078
BD0200042
BD0700135
BD0700143
BD1700313
BT075684X
BT0765877
BT0772532
BT0787697
BT0796788
C00040296
C0004043X
CH0106453
CH0106648
CH720999X
CQ4002347
CQ8121052
CX8310860
DX0002932
DX0106205
DX0108286
DX0224594
DX0231567
DX0235381
DX0235445
DX023942X
EJ6399471
EJ7505854
EJ7915976
EX9107455
EX9107965
F10406820
F29404403
FN1171306
FN1171840
FN1212622
FN1212737
FN1222310
FN1234784
FN1292044
G33830007
G33833048
这是原始数据（不光是末尾含有x，开头也有字母）

这样结果是把带有字母的全部赋值成1，

gen newvar=substr(var,-1,1)=="X"
keep if  newvar==1

是否是将所有的x替换为“000”？
数据中其它字符如何处理？

*不管X在任何位置都将其替换为“000”，其它字符不变
replace var=subinstr(var,"X","000",.)

*将所有大写字母变成“000”
forv i=65/90{
replace var=subinstr(var,char(`i'),"000",.)
}

第一次发帖能收到别人的指点，真的很感谢！这个问题我已从连老师那儿找到间接解决方案，不过还是要感谢大家的支持。