你可以使用ggplot_build来改变每一层中的linewidth和lapply，就像这样（我使用大线宽来显示结果）：

library(reReg)
library(ggplot2)
library(frailtypack)
data(readmission, package = "frailtypack")
readmission <- subset(readmission, !(id %in% c(60, 109, 280)))
mcf0 <- mcf(Recur(t.start %2% t.stop, id, event, death) ~ sex, data = readmission)
p <- plot(mcf0, conf.int = TRUE) + theme_bw(base_size = 20) 

q <- ggplot_build(p)

q$data = lapply(q$data, \(x) {
  x$linewidth = 3
  x
})

q <- ggplot_gtable(q)
plot(q)

创建于2023-04-06带有reprex v2.0.2
不同线宽：

library(reReg)
library(ggplot2)
library(frailtypack)

p <- plot(mcf0, conf.int = TRUE) + theme_bw(base_size = 20) 

q <- ggplot_build(p)

q$data = lapply(q$data, \(x) {
  x$linewidth = 1
  x
})

q <- ggplot_gtable(q)
plot(q)

创建于2023-04-06带有reprex v2.0.2